Complex sentence: The policy of the occupying power turned quickly harsh towards Ukrainians as well, the Ukrainian nationalists were driven underground; from that time forward, they fought against the Nazis, but continued also to fight against Poles and Soviet forces (see Ukrainian Insurgent Army).
Split into simpler sentences: The policy of the occupying power turned quickly harsh towards Ukrainians as well. Some of the Ukrainian nationalists were driven underground, and from that time forward, they fought against the Nazis, but continued also to fight against Poles and Soviet forces (see Ukrainian Insurgent Army).