[C19fan]

When Poland was reconstituted as a nation-state the original eastern boundary was the so called Curzon Line. The line roughly corresponded with the eastern extent of areas with a majority of Poles.
War broke out between Poland and the new Soviet Union. Poland was able to push its boundaries East including Galicia.
After the end of World War 2, the Soviet Union kept the parts of Poland it acquired from the Molotov-Ribbentropp Pact. So Galicia centered on Lvov/Lamberg is part of Ukraine.

[pierrem15]

When Poland was reconstituted as a nation-state the original eastern boundary was the so called Curzon Line.

The Brits and French drew that line. The Poles never accepted it, and in January 1919 the Polish parliament sent ultimatums to Lithuania and the Bolshevik government demanding restoration of Poland's pre-partition 1772 borders, for which they then fought.