Muscovy's southwestern expansion, particularly its incorporation of eastern Ukraine, has unintended consequences.

Most Ukrainians are Orthodox, but their close contact with the Roman Catholic Polish Counter-Reformation had also brought them Western intellectual currents.

Through Kiev, Muscovy gains links to Polish and Central European influences and to the wider Orthodox world.

Although the Ukrainian link stimulates creativity in many areas, it also undermines traditional Russian religious practices and culture.

The Russian Orthodox Church discovers that its isolation from Constantinople has caused variations to creep into its liturgical books and practices.

The Russian Orthodox patriarch, Nikon, is determined to bring the Russian texts back into conformity with the Greek originals, but Nikon encounters fierce opposition among the many Russians who view the corrections as improper foreign intrusions, or perhaps the work of the devil.

When the Orthodox Church forces Nikon's reforms, a schism results in 1667.

Those who do not accept the reforms come to be called the Old Believers (starovery); they are officially pronounced heretics and are persecuted by the church and the state.

The chief opposition figure, the archpriest Avvakum, is burned at the stake.

The split subsequently becomes permanent, and many merchants and peasants join the Old Believers.