Ukraine was apart of Russia since the time of Alexsei Romanov.. The long and short of it is the whole area up until western Europe was under the domain of the Mongols. Then in one decisive battle the yoke of the    Mongols was thrown off by a Russian. So Russia became independent while the Ukraine was still part of Poland. Then the Cossacks of Ukraine rebelled from Poland and sought alliance with the Turks and then Russia i.e. Alexsei Romanov thus became ruler of Ukraine in the 1600's. It remained a part of Russia until the start of the USSR. Then it was still part of what in the west was still called russia even though the ussr was not strictly Russia but it still was more or less the exact same thing as the empire ruled by the czars.