The Ukrainian Insurgent Army (Ukrainian: Українська Повстанська Армія (УПА), Ukrayins’ka Povstans’ka Armiya; UPA) was a Ukrainian nationalist paramilitary and later partisan army that engaged in a series of guerrilla conflicts during World War II against Nazi Germany, the Soviet Union, Czechoslovakia, and both Underground and Communist Poland. The group was the military wing of the Organization of Ukrainian Nationalists — Bandera faction (the OUN-B), originally formed in Volyn (northwestern Ukraine) in the spring and summer of 1943. Its official date of creation is 14 October 1942, day of Intercession of the Theotokos feast.

After the end of World War II, the Polish communist army — the People’s Army of Poland — fought extensively against the UPA. The UPA remained active and fought against the People’s Republic of Poland until 1947, and against the Soviet Union until 1949. It was particularly strong in the Carpathian Mountains; the entirety of Galicia and in Volyn — in modern Western Ukraine.

After Germany surrendered in May 1945, the Soviet authorities turned their attention to insurgencies taking place in Ukraine and the Baltics. Combat units were reorganised and special forces were sent in. One of the major complications that arose was the local support the UPA had from the population.

According to a 1946 report by Khrushchenv’s deputy for West Ukrainian affairs A.A. Stoiantsev, out of 42,175 operations and ambushes against the UPA by Destructive Battalions in Western Ukraine, only 10 percent had positive results - in the vast majority there was either no contact or the individual unit was disarmed and pro-Soviet leaders murdered or kidnapped. Morale amongst the NKVD in Western Ukraine was particularly low. Even within the dangerous context of Soviet state service in the late-Stalin era, West Ukraine was considered to be a "hardship post", and personnel files reveal higher rates of transfer requests, alcoholism, and nervous breakdowns and refusal to serve among NKVD field agents there at that time.

The first success of the Soviet authorities came in early 1946 in the Carpathians, which were blockaded from January 11 until April 10. The UPA operating there ceased to exist as a combat unit.[106] The continuous heavy casualties elsewhere forced the UPA to split into small units consisting of 100 soldiers. Many of the troops demobilized and returned home, when the Soviet Union offered three amnesties during 1947-1948.

The turning point in the struggle against the UPA came in 1947, when the Soviets established an intelligence gathering network within the UPA and shifted the focus of their actions from mass terror to infiltration and espionage. After 1947 the UPA’s activity began to subside. On May 30, 1947 Shukhevych issued instructions joining the OUN and UPA in underground warfare.

Source: Wikipedia, published under the GNU FDL. Retrieved 2014-03-03