Complex sentence: In one final effort to break the deadlock and end the war NATO forces planned a summer offensive across Northern Poland and into the Baltics, but the offensive ground to a halt in the face of a Warsaw Pact counterattack.
Split into simpler sentences: In one final effort to break the deadlock and end the war, NATO forces planned a summer offensive across Northern Poland and into the Baltics. The offensive ground to a halt in the face of a Warsaw Pact counterattack.