Isotalo was on sick leave and unable to take part in the first tribal expedition in the summer of 1918 due to the wounds he received in the civil war. He resigned from the army in November 1918 and recruited volunteers for the Estonian War of Independence in early 1919. The same year, he joined a group of Finnish volunteers in the Aunus expedition, the largest expedition of the tribal wars, where he led his company to victories early on and had a major role in the conquest of Olonets (Aunuksenkaupunki). His actions during this time inspired a popular song (Kuularuiskulaulu), but his victories had no long-term impact as the expedition eventually ended in defeat, partly due to a lack of support from the Finnish government.