Original sentence: Although the Cossacks were defeated in 1651 in the battle of Beresteczko, their rebellion gave opportinity to the Russians to invade and occupy the eastern half of the Polish-Lithuanian Commonwealth in 1655
Edited sentence: Although the Cossacks were defeated in 1651 in the battle of Beresteczko, their rebellion gave opportinity to the Russians to liberate their East Slavic brethren from the Polish yoke 1655