In 1914, after the outbreak of World War I and the initial defeats of the troops of the Austro–Hungarian Monarchy in its province, and at the same time the crown land, Germ. Königreich Galizien und Lodomerien (Eng. Kingdom of Galicia and Lodomeria), after the occupation of Stanislaviv by the Russians, forced to discontinue learning due to the closure of the gymnasium by the Russians. Returned to the gymnasium in 1915, after the Russian defeat by the troops of the Central Powers, i.e. the Austro–Hungarian Monarchy and the German Empire, in the Battle of Gorlice in 05.1915, and the shifting of the fighting front to the line of the Strypa River, c. 50 km east of Stanislaviv. In 1916, finished gymnasium, but did not take the final exam (i.e. matura) because on 04.06.1916, a great Russian offensive began, which went down in history as the Brusilov Offensive. It was the largest battle during World War I in terms of human losses on both sides — on the side of both the Central Powers and Russia, the losses in killed, wounded, and missing reached c. 1,000,000‐1,500,000 soldiers. During it, the Russians managed to shift the battlefront several dozen kilometers to the west, forcing the Central Powers to move powerful forces from the Western Front. On 11.08.1916, the Russians entered Stanislaviv again.

Was no longer there, however. Was drafted into the Austro–Hungarian Army and sent to a cadet school in Vienna. There also passed his matura exams. Remained in the Austro–Hungarian Army until the end of World War I, although it is not known where served. After the defeat of the Central Powers and the dissolution of the Austro–Hungarian Monarchy, became a soldier of the Ukrainian Galician Army UAH, the armed forces of the proclaimed West Ukrainian People's Republic ZUNR. Took part in the battles for and the siege of Lviv 01.11.1918‐14.05.1919, against the troops of the reborn Poland. The unit in which fought was probably part of the so‐called Operational Group „UAH‐North”, which attacked Lviv from the north, simultaneously trying to break through the supply corridor from central Poland held by Polish forces, e.g. from Przemyśl to Lviv. There, in the spring of 1919, during the fighting for the town of Yaniv, c. 25 km west of Lviv, was wounded in the head.

He stayed in a field hospital in Zhovkva, c. 25 km north of Lviv, under the care of, i.a. the de facto chaplain of the UAH, Fr Severin Stephen Baranyk OSBM. Remained under the care of the Basilian Fathers OSBM, even after 16.05.1919, when Zhovkva was recaptured by the Polish army — as part of the decisive Polish May offensive under the command of General Joseph Haller, which led to the pushing of Ukrainian troops out of Galicia — and Fr. Baranyk was interned by the Polish authorities.

After recovering, entered the Greek Catholic seminary in Stanislaviv and in 1923, in independent Poland, was ordained a priest.

In 1939 — perhaps even before the outbreak of World War II — began ministering in the parish of Zubrets, in Buchach County in the Polish Ternopil Voivodeship. The village of Zubrets itself is located nearby, c. 8 km north of the then border river Dniester, c. 9 km west of the aforementioned river Strypa, and c. 11 km south of the county town of Buchach. In 1939, it had an estimated population of c. 2,300 people, including c. 86% Greek Catholic Ukrainians, c. 13% Roman Catholic Poles, and barely a dozen or so Jews. However, in the entire Buchach County, there were more Roman Catholic Poles, c. 35%, c. 61% Ukrainians, and c. 3.5% Jews.

After the German and Russian invasion of Poland in 09.1939 and the start of World War II, pursuant to the genocidal German–Russian agreement of 23.08.1939, known as the Molotov–Ribbentrop Pact, confirmed on 28.09.1939 by the so‐called „Treaty on the Borders and Friendship between Germany and Russia”, also known as the second Molotov–Ribbentrop Pact, his parish found itself in the territory granted to Russia by the allies. The Russian occupation began. The Russians subjected Poles in particular to repression, arresting Polish intelligentsia, teachers, doctors, landowners, government officials, foresters, policemen, and families of Polish military personnel. Many other Poles became victims of four large waves of deportations „to Siberia”. Accounts often mention that „they came at night, without warning, and took away entire families, from infants to the elderly”. „When we went out into the yard, they allowed my mother to look into the chest — unfortunately, it was empty, because our neighbors had already emptied it. We took practically nothing, because they did not allow us to move around the house […] There were large snowdrifts and heavy frost”. In addition, 150,000–200,000 men were conscripted into the Russian army, and c. 100,000 were forced to work for Russian industry, mainly in the mines of the Donets Basin, in heavy industry plants in the Urals and in Siberia. Then the surveillance of priests and monks began. High taxes were imposed on the clergy, and religious education was removed from schools. The fate of the Greek Catholic clergy did not differ from the experiences of the Polish clergy during this period.

After the German attack on 22.06.1941 on their erstwhile ally, the Russians, the first great wave of Ukrainian hatred towards the Polish population surfaced in the area. E.g. in Yazlovets, 11 km east of his village, on the aforementioned Strypa River, when the main battlefront bypassed Yazlovets, due to the initial lack of significant German units, Ukrainians immediately took over power. They established their own „municipal board” and organized police militias, which they called the „Ukrainian Sich”. They organized a large demonstrations, supported by the local Greek Catholic priests, during which they shouted Ukr. „Смерть' Лахам та єврейкомуністом” (Eng. „death to the Poles and Jewish–communists”). It is not known whether similar events took place in Zubrets, but it is known that he supported the announcement of the Ukr. „Акт відновлення Української Держави” (Eng. „Act of Restoration of the Ukrainian State”), made on 30.06.1941, by activists of the genocidal OUN, collaborating with the Germans, in Lviv. Although the Germans quickly dissuaded Ukrainian nationalists from their hopes for a „free Ukraine” and arrested some of the main OUN leaders, he managed to dedicate a special „mound” in Zubrets in memory of the „Fighters for the Freedom of Ukraine”. A nun, Sr Sophie Matilde Ustyanowicz CSIC, later a victim of the genocidal OUN/UPA, who at that time served in the house of the Congregation of the Sisters of the Immaculate Conception CSIC in Yazlovets, wrote a significant, prophetic entry in a letter to her superior: „We must dedicate ourselves to the local population (I am talking about educational work) […] The spread of hatred towards everything Polish has completely depraved this unfortunate people. Social relations after this war will change the world even more than after that one [i.e. World War I]”.

When the Germans took over actual control in Zubrets, the village became part of the Germ. Landkreis Tschortkiw (Eng. Chortkiv County), which was part of the Germ. Distrikt Galizien (Eng. District of Galicia) of the German‐occupied and run quasi‐state called the Germ. Generalgouvernement (Eng. General Governorate), i.e. GG. Then, despite the described German reaction to the OUN action, was to become a representative of the „Ukrainian county delegation” — German–controlled — in Buchach, initially representing the Ukr. Український Крайовий Комітет (Eng. Ukrainian National Committee), i.e. UKK, and later, after its absorption, the Ukr. Український центральний комітет (Eng. Ukrainian Central Committee), i.e. UCK. This committee was the only legal representation of Ukrainian interests in the GG, which was under the control of the genocidal branch of the OUN, the so‐called OUN‐M.

At the same time, the Germans exploited the revealed anti‐Polish and anti‐Jewish resentments in a different way. The years 1941‐1943 were marked in particular by the extermination of Jews, i.e. the implementation of the genocidal plan Germ. «Endlösung der Judenfrage» (Eng. Final Solution of the Jewish Question), which in the GG had the codename Germ. «Aktion Reinhardt» (Eng. Operation Reinhardt). Active participants in it were units of the Ukrainian, collaborative Germ. Ukrainische Hilfspolizei (Eng. Ukrainian Auxiliary Police), operating as the Germ. Schutzmannschaft (Eng. Protection Battalions), i.e. Schuma — established, i.a. from the transformation of the aforementioned „Ukrainian Sich” militias – and also the Germ. Jüdischer Ordnungsdienst (Eng. Jewish Order Service). The latter was particularly active in the Buchach ghetto ‐ Jewish sources state that the local „Jewish police robbed, killed, worse than the Germans” — and there Jews Zubrets were prob. driven to. The Jews from Buchach ghetto were murdered in four so‐called Germ. Aktion (Eng. operation). The first two batches of Jews were transported to the Germ. Vernichtungslager (Eng. Extermination camp) VL Belzec on 15‐17.10.1942 and in 11.1942. The last Jews in Buchach were murdered 02.02.1943 (c. 2,000 people) and in 04.1943 (c.4,000 victims). In both of these Germ. Aktion, the Germans, with the participation of the Germ. Ukrainische Hilfspolizei, killed Jews over previously dug pits near the so‐called Mount Fedora in Buchach — the name comes from an Italian daredevil, Fedorini from Florence, who prob. in the 19th century, climbed a mountain and, on a flying machine had built, resembling a hang glider, jumped down, bounced off the mountaintop and after a smooth flight of several meters, plummeted to his death on the spot. Jewish sources state that during the Germ. Aktion in 02.1943, „the bloodshed [of the victims] was so great that the town's drinking water sources were contaminated”.

In 05.1943, the German authorities were able to declare that Buchach and the surrounding area were Germ. „Judenfrei” (Eng. „free of Jews”). This, however, was only partially true. Jewish sources describe the situation that followed the liquidation of the Buchach ghetto as follows: „The hunt for hiding Jews continued with the help of local informers. In this final phase, a certain dynamic developed in which Jews "hiding among the peasants paid high sums for shelter, and the naive peasants went to the city and bought whatever they wanted". As a result, "Ukrainian murderers […] began to follow these peasants and found Jews in attics, basements, etc. […] [and] shot them on the spot". This, in turn, sparked "mass denunciations", and "the peasants themselves began to kill Jews or evict them"”.

At that time, was not only the representative of the UCK in Buchach, but also negotiated with the Germans, acting i.a. as a translator, the minimum quotas that the inhabitants of his village had to provide — i.e. acts interpreted according to the Russian genocidal NKVD as collaboration, and according to Ukrainian sources as providing support to his parishioners. The latter also report that during the entire occupation, c. 350 people from the village and neighborhood left for forced labor.

On 1943 also supported German recruitment efforts to create the Germ. 14.

Waffen‐Grenadier‐Division der SS – ukrainische Nr. 1 (Eng. 14th Grenadier Division of the Waffen SS – 1st Ukrainian), i.e. SS‐Galizien — a battlefront‐line division subordinate to the genocidal Germ. Die Schutzstaffel der NSDAP (Eng. NSDAP Protection Squad), i.e. «SS», a paramilitary formation subordinate to the ruling National Socialist German Workers' Party NSDAP in Germany. Did this despite the fact that the ordinary of his Stanislaviv eparchy, Bp Gregory Khomyshyn, opposed the nationalist and genocidal policies of the OUN. According to the Polish Institute of National Remembrance, i.e. IPN „opposed the decree of the German occupation authorities regarding the involvement of Greek Catholic priests in the creation of the SS‐Galizien Division, forbidding priests from leaving their jobs in parishes and serving as chaplains of the division”. The Greek Catholic Metropolitan of Lviv, Abp Andrew Sheptytsky, did exactly the opposite.

This was happening at a time when in Volyn, c. 200 km to the north, the OUN had established the genocidal militant organization OUN/UPA.

And already in 02.1943 Roman Shukhevych, nom de guerre „Taras Chuprynka”, the chief commander of the OUN/UPA, who in 1941 was a member of the Ukrainian Germ. Sondergruppe Nachtigall (Eng. Special Group Nightingale) — a unit of the Germ. Wehrmacht (Eng. Armed Forces) that took part in the German attack on Russians in 1941, accused of participating in the Jewish pogrom in Lviv in 1941 — and later a member of the Germ. Schutzmannschaftsbataillon 201 (Eng. 201st Protection team Battalion) — responsible for the murder of Jews and civilians in the territory of Belarus — issued an order: „The extermination operation should be carried out according to the following principles: Polish villages are to be burned, and their populations massacred. Attacks on towns will take place in broad daylight, not at night. In mixed villages, the Polish population alone should be liquidated, and farmsteads should be burned only if they are 15 meters away and when there is no risk of the fire spreading to neighboring Ukrainian buildings. The Ukrainian population will receive instructions as to where to gather during the attack […] For every Ukrainian murdered, whether by Poles or Germans, 100 (one hundred) Poles will be executed”.

It was the de facto signal for the commencement of the «Genocidium Atrox» — i.e. the genocide perpetrated by Ukrainians, known as „Volyn genocide”.

Immediately thereafter, in 03.1943, the UPA issued an appeal to members of the Germ. Ukrainische Hilfspolizei to desert and join the UPA ranks. Perhaps as many as 10,000 Ukrainians did so.

The tactics of the genocidal Ukrainians were detailed in an order issued by the UPA commander in Volyn, Dmytro Klachkivsky, nom de guerre „Klym Savur”, in 06.1943. Anticipating Germany's defeat in the war with Russia, explained and ordered: „We should carry out a major operation to eliminate the Polish element. When the German troops withdraw, we should use this opportune moment to eliminate the entire male population aged 16 to 60 […] We cannot lose this fight, and we must weaken Polish forces at all costs. Forest villages and villages located near forest massifs should disappear from the face of the earth”.

Volyn was drenched in Polish blood. Tens of thousands of Poles were murdered by the Ukrainians — with German passivity — in an extremely barbaric manner. Hundreds of villages were burned.

When, at the turn of 1943/1944, it became clear that Germany was losing the war in the East — on 24.12.1943, a major Russian offensive, known as the Dnieper–Carpathian Operation, began, which rapidly began to shift the battlefront of the Germ‐Russian fighting, e.g. towards Lviv, Ternopil and Stanislaviv — the OUN/UPA decided to extend the genocide «Genocidium Atrox» to the Germ. Distrikt Galizien. Until then, the groups operating there — in order not to „annoy” the Germans — were mainly operating under the euphemistic name Ukr. Українська Народна Самооборона (Eng. Ukrainian National Self‐Defense), i.e. UNS, and later also Ukr. Самооборонні кущові відділи (Eng. Self‐Defense Unit), i.e. SKW, reinforced by deserters from the Germ. Ukrainische Hilfspolizei and Schuma, seasoned in the genocide of Jews. The Ukrainian génocidaires then formed, i.a. the OUN/UPA operational group „UPA‐West”, under the command of Vasyl Sydor, nom de guerre „Shelest” — a degenerate with a similar career path as his superior, the aforementioned génocidaire, Roman Shukhevych, i.e. from the Germ. Sondergruppe Nachtigall, through the Germ. Schutzmannschaftsbataillon 201, where both gained experience in the extermination of Jews — who ordered „continue to strike at Poles until they are destroyed to the last one from these lands”.

In the Zubrets region, attacks on Poles had occurred earlier — e.g. in 03.1943, Ukrainians murdered 24 Poles in Zolotyi Potik, c. 12 km away — but from the turn of 1943/1944, they began to have a systemic character. All Poles were at risk. Initially, until 04.1944, these were individual attacks, on houses and their inhabitants — and so, e.g., in 12.1943, in Barysh, c. 6 km away, 9 Poles were murdered, including the headmaster of a primary school: he was murdered by his Ukrainian students; on 01.01.1944, in the same Barysh, another 6 Poles were murdered; and in 04.1944, in Skomorokhy, c. 12 km away — he already held then the additional function of administrator of this parish, as well as administrator of the nearby parish of Trybukhivtsi — a Polish family of four.

The murders stopped in 04.1944, because at the end of 03.1944 the Buchach region was occupied by the Russians. For a short time, for on c. 07.04.1944, the Germans launched a counterattack. It coincided with the end of the Dnieper–Carpathian Operation by the Russians and the suspension of battlefront‐line fighting for the spring period. The Germans managed to push the Russians to the northeast, beyond Buchach, and the area became a frontline area. After a few months, the Russians launched a new offensive, i.e. the Lviv–Sandomierz Operation, and on c. 21‐22.07.1944, entered Buchach and his Zubrets parish. The Russian occupation began.

Attempted, it seems, to escape from the village before the arrival of the Russians — the Germans provided him with a car in which left Zubrets with the village mayor — but after some time, under unknown circumstances, returned.

According to Ukrainian sources, the Russian genocidal NKVD conducted some investigation into him, but was never arrested.

Meanwhile, however, the genocidal OUN/UPA, after six months of „laying low”, adapting to the changed conditions — after all, it no longer had tactical support, or at least neutrality, from the Germans, and the Russians treated the OUN/UPA as an enemy — launched another wave of attacks on the Polish community in late 1944. The decisions of the Tehran Conference of 28.11‐01.12.1943, when the treacherous British and Americans agreed to establish the post‐war Polish border along the Curzon–Namier Line, i.e. de facto recognition of the legitimacy of the Russian invasion of Poland in 09.1939 and recognition of Russian claims expressed in the Molotov–Ribbentrop Pact of 1939, were not yet known. The Yalta Conference of 04‐11.02.1945, when the Allies and the Russian occupier had formally decided to move the Polish border westward, to the line of the Bug River, had not yet taken place. But signals about the upcoming new order were already reaching both Poles and Ukrainians. The OUN/UPA therefore intensified its genocidal anti‐Polish campaign.

Already on 23.08.1944, in Rusyliv, c. 9 km away from Zubrets, Ukrainians kidnapped and murdered two nuns, the above‐mentioned Sr Sophie Matilde Ustyanowicz CSIC and Sr Laetitia Wanda Szembek CSIC. On 15.01.1945, in the above‐mentioned Skomorokhy, they murdered 7 young Poles. On 02.02.1945, in the village of Porokhova, c. 5 km away, they murdered 5 Poles. On 05‐06.02.1945, the greatest crime took place — in aforementioned Barysh 135 Poles were cruelly murdered. On 07.02.1945, the same gang murdered another 37‐70 Poles in Zalissya, c. 10 km away from his Zubrets. And in 03.1945, in Lishchantsi, c. 9 km away, 22 Poles were murdered.

Genocidal attacks on Barysh and Zalissya were carried out by the OUN sotnias Ukr. „Чорноморці” (Eng. „Black Sea Fighters”) and Ukr. „Сірі вовки” (Eng. „Grey Wolves”), under the command of the kuren leader Peter Khamczuk, nom de guerre Ukr. „Бистрий” (Eng. „Bystry”), which a few days earlier had murdered 65‐125 Poles in Chervonohorod, c. 30 km away. They organized their base in the vicinity of his Zubrets, where they returned after the murders. After a few days of „rest”, on 12‐12.02.1945, Khamczuk's génocidaires attacked Puźniki, c. 6 km away from Zubrets, and murdered another c. 100 Poles.

These events, it seems, shocked him. This is evidenced by brief records in Polish sources stating that he protested against the murders of Poles. It is not known how did it — whether expressed it privately or took advantage of his position as parish priest of a Greek Catholic parish — but this act of defiance became his death sentence at the hands of the OUN/UPA génocidaires.

His stance in the Greek Catholic Church after the arrest of its ordinary, Bp Gregory Khomyshyn, by the Russians in 04.1945 can also be considered an expression of defiance — albeit expressed in the form of apostasy. A certain Fr Anthony Pelwecki became the temporary administrator, with the consent of the Russian occupier, of the Stanislaviv Eparchy. Began then collaborating with the „Initiative Group for the Reunification of the Greek Catholic Church with the Orthodox Church”, founded i.a. by Fr Pelwecki — an initiative of apostasy by Greek Catholics, controlled by the genocidal NKVD and its successor, the MVD. And Fr Pelwecki appointed him dean of the Buchach deanery.

Both acts were considered acts of treason by the genocidal OUN/UPA.

The report of the criminal Russian MVD from 08.01.1946 describes his death as follows: „On December 31, 1946, at 11 p.m., there was a knock on the apartment of Ivan Yuriyovych Tereshkun, a priest of the Greek Catholic Church in the village of Zubrets, Zolotyi Potik district, Ternopil region, born in 1897, a Ukrainian with a higher theological education, and when the housewife answered, the unknown man knocking said: "The commander of the military unit wants to speak to the priest".

[…] Two armed men dressed in Red Army uniforms entered the priest's apartment. The housewife was immediately thrown out of the apartment.

Then they took Father Tereshkun, to the center of the village and hung him on a tree on a wire.

A sign was hung around Tereshkun's neck, written in red pencil on paper, glued to the board: "For the betrayal of Christ and the people", signed "SB".

All of Tereshkun’s household belongings were taken away by bandits. That same night, a local resident, manager of a […] shop, was hanged next to Tereshkun.

Tereshkun’s body was taken away by the residents and on January 3, 1946, he was buried”.

The aforementioned „SB” is a reference to the Ukr. Служба Безпеки (Eng. Security Service), i.e. SB OUN, of the genocidal OUN, tracking down political and ideological opponents of the OUN, carrying out their physical liquidation, and also participating in the murders of the Polish population. Sources state that „SB OUN could only issue death sentences to "enemies of the Ukrainian nation" […] For minor offenses, the so‐called "buki" were used, i.e. beatings with beech sticks 10 to 50 times. Major offenses were punished by death. The sentence was carried out by shooting or hanging […] some group commanders "chopped off the heads of their victims"”. SB OUN was founded back in 1940, in the GG, under the watchful care of the Germans, and training was conducted, among others, in Zakopane, at the „Stamary” hotel. According to the contemporary website of this hotel, „the training included the principles of sabotage, sabotage, Gestapo interrogation methods and killing methods”. At the same time, i.e. on 20.02.1940, in Zakopane, in the villas „Pan Tadeusz” (Eng. „Sir Thaddeus”) and „Telimena”, the third so‐called „thematic conference” began between the Germ. Geheime Staatspolizei (Eng. Secret State Police), i.e. the Gestapo, and the Rus. Народный Комиссариат Внутренних Дел (Eng. People's Commissariat of Internal Affairs), i.e. the NKVD, two genocidal allied organizations, debating cooperation and ways of combating and exterminating Poles in the territories they occupied. In Zakopane, all these undertakings were supervised by the Gestapo, which had its headquarters in the „Palace” villa, where Polish patriots were being murdered.

And in 1946, the centuries‐long presence of millions of Poles in the so‐called Eastern Borderlands of the Poland, marked by the construction of hundreds of cities, infrastructure, and educational and administrative institutions, i.e. in Galicia, came to an end. The Russians, in accordance with their standard practice of resolving social and political conflicts in conquered territories, deported Poles westward, to territories that had belonged to Germany before World War II.

They euphemistically called this procedure „repatriation”, to mislead the gullible West.

On 12.10.2007, the génocidaire Roman Shukhevych was posthumously awarded the title of Hero of Ukraine. In 12.2020, the Verkhovna Rada of Ukraine, in a resolution, recognized génocidaire Dmitry Klachkivsky as „the leader of the Ukrainian Insurgent Army in Volyn and a participant in the struggle for Ukraine's independence in the 20th century”. On 10.12.2017, on behalf of the „Coordination Council for the Commemoration of Decorated Knights of the OUN and UPA”, génocidaire Vasyl Sydor was posthumously awarded in Lviv the Silver Cross of Military Merit of the UPA, 1st Class (No. 009). On 20.11.2017, in Chortkiv, the family of the génocidaire Peter Khamchuk was handed in the orders awarded to him posthumously: the Bronze Cross of Military Merit of the UPA (No. 023) and the Silver Cross of Military Merit of the UPA, 1st Class (No. 013). In several locations, monuments and commemorative plaques have been erected to these Lat. „hostis humani generis”, the schools were named after them — e.g. in 2014, the Ukrainian state erected a monument in Chortkiv to the génocidaire Piotr Khamchuk.

Lat. „O Tempora! O mores!”