Read this article and answer this question Galicia-Volhynia Wars were several wars fought in the years 1340-1392 over the succession in the Principality of Galicia-Volhynia . After Boleslaw-Yuri II was poisoned by local nobles in 1340, both Grand Duchy of Lithuania and Kingdom of Poland advanced claims over the principality. After a prolonged conflict, Galicia-Volhynia was divided between Poland  and Lithuania  and the principality ceased to exist as an independent state. Poland acquired a territory of approximately 52,000 square kilometres  with 200,000 inhabitants.
When did Galicia-Volhynia cease to exist?