The Moscow Metropolitan Greek Foty, who stood for monocracy of the Grand Duke of Moscow, died in 1431. After his death the Razan Bishop Ion was consecrated metropolitan by the Russian Church Leaders in response to the wishes of Vasily II. However the Constantinople Patriarch did not approve his candidature since long before his arrival to Constantinople the Patriarch had appointed to the same position the Smolensk Bishop Gerasim. In the autumn of 1433 Gerasim returned from Constantinople to Smolensk, which belonged to the Great Lithuanian Princedom. He refused to go to Moscow saying that Russian princes levied internal war for the Grand Duke's throne.
Gerasim was accused of treachery and perished in Smolensk in 1435. Ion went to Constantinople for the second time. But he was late again - the Patriarchate had appointed Greek Isidor, an outstanding religious figure and highly educated person, even before Ion reached the city. In April, 1437 the new Metropolitan Isidor arrived to Moscow.
Assignment of Isidor had the aim to provide acceptance of planned Orthodox-Catholic Union by the Russian Church. That time Byzantium was in mortal danger from the Ottoman Empire. Trying to save the remains of the State, the Byzantian Emperor entered into negotiations with the Pope. He wanted to receive powerful backing from European States against the Turks and raised a question of association of the churches. The Pope Eugene IV, in his turn, willingly responded to the offer of Byzantium, expecting to strengthen prestige of papal authority by the Union.
Metropolitan Isidor took active participation in the conclusion of the Union that was signed in Florence in 1439. The Papal Curia and the Constantinople Patriarchate signed the act of acceptance of catholic doctrines by the Orthodox Church and recognition of the Pope as the head of the Church with reservation of orthodox ceremonies in public worship.
On his way from Florence to Moscow Isidor dispatched the vicarial messages informing about the Union to the Polish, Lithuanian and Russian Lands. However tolerant attitude towards the Union Isidor met only in Kiev and Smolensk. In the spring of 1441 the Metropolitan arrived to Moscow with a letter from the Pope to Vasily the Dark. But the Grand Duke refused to recognize the act of association of the churches and proclaimed Isidor a heretic. The latter was arrested and cloistered in the Chudov Monastery. From there the Metropolitan fled first to Tver, then to Lithuania and, at last, to Rome.
Exile of consecrated by Constantinople metropolitan and denial of the Church Union of 1439 had significant consequences. On the one hand, the belief that the Greeks betrayed orthodox confession for the sake of their lucrative impulse was growing among Russian clergy, and on the other hand, the person of the Grand Duke became more and more associated with the image of the true protector of the belief.
In 1448 a council of clergy leaders in Moscow appointed Ion, the protege of Vasily II, to the post of the metropolitan without any sanction of the Constantinople Patriarch. This act marked the end of dependence of the Russian Church from Byzantium (autocephaly). At the same time, from this moment, the Moscow Metropolia became directly dependent from the Grand Duke's power.