Complex sentence: Haller's Army changed the balance of power in Galicia and in Volhynia, and its arrival allowed the Poles to repel the Ukrainians and establish a demarcation line at the river Zbruch on May 14,1919.
Split into simpler sentences: Haller's Army changed the balance of power in Galicia and in Volhynia. Its arrival allowed the Poles to repel the Ukrainians, and establish a demarcation line at the river Zbruch on May 14,1919.