Russia has always felt surrounded, and land locked. Yes they took the Baltic area from the old Swedish empire which controlled Finland and the Baltic states also. Russia wanted an outlet to the sea and took the St. Petersburg area from Sweden. They later conquered the 3 Baltic states of Estonia, Latvia, and Lithuania. They later turned south and took Ukraine, Belarus, and the area on the northern coast of the Black Sea from the Turks. The also crossed the Eural Mountains and took Siberia. Then they pushed into Central Asia and the Caucasian Mountains area again from the Turks. Anyway, this became the Russian empire, which later fell to the communists. Ukraine has independence shortly after WWI when Germany occupied them until the communists took Ukraine and merged it again to Russia. Ukraine sided with the Germans in WWII because of how Stalin purged them and killed 20-30 million Ukrainians to take their lands and make soviet collectives out of them. They killed the landowners or whoever stood in their way. They therefore hate the Russians. My wife's family is from the Ukraine and hate the Russians. Her grandparents came here to get away from the Russians and Stalin in particular.
