Complex sentence: The Kinchō army, out of necessity, returned the attack, starting the war again, but Yashima no Hage-tanuki stepped in to mediate, and the war finally ended.
Split into simpler sentences: The Kinchō army, out of necessity, returned the attack, thus starting the war again. But Yashima no Hage-tanuki stepped in to mediate, and the war finally ended.