In 1965, the first US troops in Vietnam landed and the Military Assisting Command Vietnam (MACV) was commissioned to develop a strategy for the US military. Both within MACV and beyond, the use of an indirect counterinsurgency method (COIN) was promoted, focusing on winning over the local population. Instead, MACV chose a direct COIN method that instead focused on defeating the opponent on the battlefield. The US military never reached the success that sought in the Vietnam War, and some argue that the reason for the failure was in the choice of strategy. Several studies attempts to explain MACV's choice of strategy in the Vietnam war with institutional learning and leadership identified as likely explanations. At the same time, there is a lot of research where organizations behavior is explained by similarity to other organizations. If organizations' behavior can be explained by their tendency to imitate each other, can it explain MACV's choice of strategy in Vietnam? The purpose of this study is to investigate why MACV chose a direct COIN method. As a basis for the study, three theories about institutional isomorphism by Powell and DiMaggio are used. The conclusion of the study is that the three theories in combination can contribute three possible explanations to MACV's decision on a direct COIN method. The first is the lack of clear directions from the government to MACV, the other is MACV's tendency to mimic their own as well as others' organizations and the third is internal equity in staff.