The History of Poland: Every Year - YouTube Why Poland? You'll see.
In its first few centuries, Poland was roughly in its present boundaries. Then in 1385, Poland and Lithuania conquered what is now Belarus and W Ukraine. Then in 1404, the Polish-Lithuanian Commonwealth conquered most of Ukraine and a bit of Russia just east of Belarus. In 1500, the PLC lost a bit of Ukraine near Kiev, and in 1522, that Russian strip east of Belarus. In 1529, it lost southern Ukraine near Odessa, and in 1634, it got back that Russian strip. In the 1650's, it lost most of its territory, but by 1665, it got most of its old territory back, most of Belarus and W Ukraine.
Poland was partitioned in 1772, 1793 and 1795, disappearing off of the map in the third partition.
The nation became independent again in 1918, after WWI, extending into W Belarus and the W end of Ukraine. It disappeared off of the map by being conquered by Germany in WWII, but became independent again afterward, in 1945, in its present boundaries.
So western Ukraine was ruled by Poland for over 3 1/2 centuries.