This thesis is a study on the use of military force in United States peacemaking in Lebanon between 1982 and 1984. It argues that the failure of the Reagan Administration to understand accurately the complex political landscape of the Lebanese Civil War resulted in the US and the Multinational Force in Beirut becoming intertwined in the broader Lebanese conflict. Because of this, President Ronald Reagan and Secretary of State George Shultz applied a policy focusing on military force with a vague peacekeeping vision which led to catastrophic US casualties. This thesis also argues that US policy in Lebanon was inaccurately designed because, from the outset, Washington did not see Lebanon as a key policy frontline. However, the Administration’s failed attempts to resolve the crisis and Reagan’s personal pursuit for international credibility bound the US to one of the world’s most complicated and violent conflicts. By examining newly released archival material this thesis will show how the foundations of the US’ interventionist policy in Lebanon came from the Reagan Administration’s desire to see the US as the key military power in the Middle East rather than protecting Lebanese sovereignty or containing the Soviets. This thesis offers a fresh perspective on the impact of the US intervention and the decisionmaking drivers that led Reagan into the Lebanese Civil War. It challenges the notion that Reagan deployed US Marines under the ideals of international peacekeeping. Rather it will argue that the Multinational Force withdrew from Lebanon as a failed military force having made little progress.