Zagonyi was a Hungarian soldier of fortune who served in Europe before he came to America and "sold his sword" to the Union forces. In command of General Fremont's body guard, with 300 troops, he attacked the Confederates in Springfield in advance of Fremont's main forces. He returned to Fremont's encampment near Bolivar. Three days later, on October 29th, Fremont reached Springfield, marching about 30 miles in 12 hours. Zagonyi shared in command of the Union troops who attacked Springfield. When Fremont assumed command of the Mountain Department in West Virginia in early 1862, he became his chief of cavalry with the rank of colonel. When Fremont resigned in 1862, he was put on the inactive list along with Zagonyi, and neither of them saw any more service in the war.