sentences:  Following Mongol invasion of Rus', which weakened Ruthenian states, the Grand Duchy of Lithuania, a new power in Eastern Europe, occupied Chełm.In 1340, the town was annexed by Polish King Kazimierz Wielki, together with Belz, Red Ruthenia and Podolia.At first, the Land of Chełm was united with the Land of Belz, but in 1387, King Wladyslaw Jagiello handed Belz as a fief to Duke of Mazovia Siemowit, while Chełm was directly annexed by the Polish Crown.