History of the Middle East during the Cold War is replete with examples of external military intervention by superpowers and their clients. In the 1970s a protracted civil conflict in Lebanon took a particularly tragic turn. The present paper examines the preparation and the conduct of the Operation Peace for Galilee, also known as the First Lebanon War, in the context of the U.S.-Israeli relations with the help of level-of-analysis approach. The first section depicts a political landscape in both the United States and Israel in the early 1980s. Drawing political portraits of the leaders of two countries, the author concludes that their personal relations had a crucial impact on the positions of the United States and Israel and determined the scale and character of two countries’ involvement in the Lebanese crisis. The paper provides a detailed examination of reasons and motives behind the Israeli leaders’ decision to intervene militarily in the civil war in Lebanon, focusing on the Israeli-Syrian contradictions and terrorist activities of the Palestine Liberation Organization. The author emphasizes that deep divisions between the U.S. and Israel became apparent from the very outset of the crisis. Whereas the United States, although not always consistently, called on Israel to show restraint, political and military leaders of the Jewish State opted for a military solution. The second and third sections review the course and outcomes of the Operation Peace for Galilee and its impact on the U.S.-Israeli relations. The author emphasizes that actions of the Israeli army provoked a split within the Jewish community in the United States, with many of its leaders condemning Israel’s actions and calling for an immediate end to the use of violence. As a result, the First Lebanon War became a serious trial for the U.S.-Israeli strategic partnership, forged during the Cold War, and provoked an internal crisis in Israel. The Operation Peace for Galilee had a very limited success, once again demonstrating negative implications of external military intervention in the internal affairs of sovereign states.