Complex sentence: The transfer was described by some of the Supreme Soviet as a gift to commemorate the 300th anniversary of the Treaty of Pereyaslav in 1654 when the Cossack Rada apparently decided to unify with Muscovy, putting in place the eventual acquisition of Ukraine by Russia.
Split into simpler sentences: The transfer was described by some of the Supreme Soviet as a gift to commemorate the 300th anniversary of the Treaty of Pereyaslav. The treaty of 1654 when the Cossack Rada apparently decided to unify with Muscovy, so putting in place the eventual acquisition of Ukraine by Russia.