In April 1778, Brant returned to Onoquaga. He became one of the most active partisan leaders in the frontier war. He and his Volunteers raided rebel settlements throughout the Mohawk Valley, stealing their cattle, burning their houses, and killing many. The British historian Michael Johnson called Brant the "scourge of the American settlements of New York and Pennsylvania", being one of the most feared Loyalist irregular commanders in the war. Morton wrote the fighting on the New York frontier was not so much between Americans and the British as "a cruel civil war between Loyalist and Patriot, Mohawk and Oneida, in a crude frontier tradition". On May 30, Brant led an attack on Cobleskill. At the Battle of the Cobleskill, Brant ambushed an American force of 50 men, consisting of Continental Army regulars and New York militiamen, killing 20 Americans and burning down the farms. In September, along with Captain William Caldwell, he led a mixed force of Indians and Loyalists in a raid on German Flatts. During the raid on German Flatts, Brant burned down almost the entire village, sparing only the church, the fort, and two houses belonging to Loyalists. Brant's fame as a guerrilla leader was such that the Americans credited him with being behind any attack by Loyalist Haudenosaunee, even when he was not. In the Battle of Wyoming in July, the Seneca were accused of slaughtering noncombatant civilians. Although Brant was suspected of being involved, he did not participate in that battle, which nonetheless gave him the unflattering epithet of "Monster Brant".