Original 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
Edited sentence: Although the Cossacks were defeated in 1651 in the battle of Beresteczko, their rebellion gave pretext to the Russians to invade and occupy the eastern half of the Polish-Lithuanian Commonwealth in 1655