Complex sentence: In 1918, the city was declared part of the short-lived Belarusian Democratic Republic, then Podolia Governorate of Ukraine, to finally within Poland's borders following the Polish-Soviet War; a development that was formally recognized by the Treaty of Riga in 1921.
Split into simpler sentences: In 1918, the city was declared part of the short-lived Belarusian Democratic Republic. The city changed hands twice during the Polish-Soviet War and eventually stayed inside Polish borders, a development that was formally recognized by the Treaty of Riga in 1921.