Complex sentence: AK in the Białystok area was a powerful force, in early 1945 it had almost 30 000 soldiers, together with units that remained east of the Curzon Line, around Grodno and Wolkowysk.
Split into simpler sentences: AK in the Białystok area was a powerful force. In early 1945 it had almost 30,000 soldiers, together with units that remained east of the Curzon Line, around Grodno and Wolkowysk.