It was part of Kievan Rus until the confederation of principalities collapsed. It then was a kingdom (the Kingdom of Galicia Volyhnia) and was heavily influenced by the Latin European world, including Poland. They were an East Slavic people who were in contact with Latin Catholic civilisation.
Eventually Galicia Volhynia was absorbed into the Polish kingdom but later emerged in the 1600s in the form of the Cossack Hetmanate.
When Muscovy began expanding and creating the modern Russian state it encountered very little resistance from Novgorod, Pskov and others. However Ukraine was never fully assimilated and the Ukrainian identity remains strong even to this day.
Why out of all the former constituent principalities of Kievan Rus did the land that is now Ukraine develop such a strong and independent identity? Why did Novgorod not develop a similar identity and why was it so easily absorbed by Muscovy?