Complex sentence: During the Polish-Ukrainian War, the army of the West Ukrainian People's Republic was able to hold off Poland for approximately nine months but by July 1919, Polish forces had taken over most of the territory claimed by the West Ukrainian People's Republic.
Split into simpler sentences: During the Polish-Ukrainian War, the army of the West Ukrainian People's Republic was able to hold off Poland for approximately nine months. By July 1919, Polish forces took over most of the territory claimed by the West Ukrainian People's Republic.