This led to a rebellion of the more democratic cossacks Martyn Pushkar and Yakiv Barabash a civil war that cost about 50,000 lives .
Yakiv Barabash was defeated in June 1658 .
This led to a rebellion of the more democratic cossacks Martyn Pushkar and Yakiv Barabash , which was defeated in June 1658 , a civil war that cost about 50,000 lives .