Union of Brest
The Union of Brest refers to the 1595-1596 decision of the (Ruthenian) Church of Rus', the Metropolia of Kiev-Halych and all Rus', to break relations with the Patriarch of Constantinople and place itself under the Pope of Rome in order to avoid being ruled by the newly established Patriarch of Moscow. At the time, this church included most Ukrainians and Belarusians, under the rule of the Polish-Lithuanian Commonwealth. The hierarchs of the Kievan church gathered in synod in the city of Brest to compose the union's 33 articles, which were then accepted by the Roman Catholic pope. At first widely successful, within several decades it had lost much of its initial support. In Austrian Galicia, however, the church fared well and remains strong to this day, most notably in the Ukrainian Greek Catholic Church.
The union was strongly supported by the king of Poland and grand duke of Lithuania, Sigismund III Vasa, but opposed by some bishops and prominent nobles of Rus' and perhaps most importantly by the nascent Cossack movement for Ukrainian self-rule. The result was "Rus' fighting against Rus'" and the splitting of the Church of Rus' into Greek Catholic, also known as Uniate and Orthodox jurisdictions.
A large area in the southwest of Russia became absorbed by Lithuania and Poland after the destruction of Kievan power by the Tartars. This southwestern part of Russia was commonly known as Little Russia or the Ukraine. In 1386, the kingdoms of Poland and Lithuania were united under a single ruler. The monarch of the united realm was Roman Catholic, and a substantial minority of the population were Russian and Orthodox. These Orthodox were in a tight spot because the Patriarch of Constantinople, to whose jurisdiction they belonged, could exercise no control in Poland. The bishops were appointed not by the Church but by the Roman Catholic king of Poland.
The authorities in Poland always tried to make the Orthodox submit to the pope to reunify Christianity. With the arrival of the Jesuits in 1564, pressure on the Orthodox increased. Secret negotiations with the Orthodox bishops, the nominees of Roman Catholic monarchs, were used to "unite" them with Rome without the faithful’s knowledge. But instead it led to a council being summoned at Brest-Litovsk to proclaim the union with Rome publicly.
At this synod six out of eight Orthodox bishops, including the Metropolitan of Kiev, Michael Ragoza, supported the union, but the remaining two bishops, together with a large number of the delegates from the monasteries and from the parish clergy, desired to remain members of the Orthodox Church. The two sides concluded by excommunicating and anathematizing one another.
The government recognized only the decisions of the Roman party at the Council of Brest, so from their point of view the Orthodox Church in Poland had now ceased to exist. Against the wishes of the monks and congregations, monasteries and churches were forcibly seized and given to the Uniates.
This attempt for the unity of Christendom backfired, and the Union of Brest has further embittered relations between Orthodoxy and Rome from 1596 until the present day. The main sore point is the that, from the Orthodox point of view, the Jesuits began their quest for union through deceit and then resorted to violence.