But he strongly opposed the treaty because it restored the union with Poland, and annulled the Pereiaslav articles, which he favored more of a pro-Russian orientation.

In 1661 he led a revolt against Yurii Khmelnytsky with left-bank regiments, and Zaporozhian otaman Ivan Briukhovetsky.

During the Russo-Polish War he fought against the Poles, and the Crimean Tatars, in order to re-unite all of the Cossack lands under his reign.

But Russia started seeking aid from Somko's opponents, in particular Ivan Briukhovetsky who supported Russian rule, in turn started accusing Somko of secret negotiations with Khmelnytsky, and Pavlo Teteria, which caused a delay in the final decision of the Cossack starshyna council at Kozelets in 1662 to recognize his tenure as hetman.

The officers proposed him and colonel Vasyl Zolotarenko of the Nizhyn Regiment as candidates, but the majority and including the Tsar supported Briukhovetsky and elected him the new hetman.