Orientales omnes Ecclesias (December 23, 1945) is an encyclical of Pope Pius XII to the faithful of the Ukrainian Greek Catholic Church.

In his encyclical, Pope Pius XII explains that many trials and persecutions took place in the last three hundred and fifty years, but that the Ukrainian Greek Catholic Church always came out strong.

After World War II, in 1945, Polish and Slovakian areas became part of the Soviet Union which exerted pressure, on the Ruthenians and other Ukrainians united with Rome, to sever relations and join the Orthodox Church headed by the Patriarch of Moscow.

He also was aware that, in months preceding the encyclical, all Catholic bishops of the Ukrainian Church had been arrested, including Josyf Slipyj, Gregory Chomysyn, John Laysevkyi, Nicolas Carneckyi and Josaphat Kocylovskyi.

On July 1, 1945, some three hundred priests of the United Church wrote to Molotov; they protested the arrest of all bishops and large parts of the Catholic clergy.

[8] In order to address this problem, Pius decided to engage in a comprehensive historical review of the reunion and its advantages to the faithful in Ukraine.

Towards the end of the 16th century, it became obvious that there was no hope of achieving renewal and reform of the Ruthenian Church except by restoring union with the Apostolic See.

[10] At the end of the nineteenth and the beginning of the 20th century, economic conditions led to the emigration of many from Galicia to the US, Canada and South America.

Pope Pius X feared that these emigrants may lose heir religious identity, and in 1907 he appointed a bishop with special faculties for them.

Rusyns on the other side of the Czechoslovak border were also forced to become Orthodox, while those in the Polish Lemko region were deported en masse in 1947 either to the Soviet Union or to other parts of Poland.