This thesis analyzes the history and importance of military cooperation between Greece and the United States of America (USA) with a focus on the Mutual Defense Cooperation Agreement (MDCA), covering developments since its inception in 1990 up to 2024. The MDCA has been an important forum for bilateral relations covering mutual interests related to regional stability and security cooperation between both countries as well as strategic developments in the Eastern Mediterranean. It is true that Athens enjoys pivotal relations with Washington going back to the aftermath of World War II (WWII) and reaching maturity through events such as the formation of the Truman Doctrine in support for Greece or its entrance into the North Atlantic Treaty Organization (NATO) in 1952. This formed the basis of assistance from the U.S. military during important time periods such as the post-WWII era (Cold War) and then over the years under a repressive military Junta regime, helping Greece foil attempts by communism to advance its influence in Europe through Greece's borders. The paper outlines how U.S. military activity in Greece has supported regional security efforts, highlighting Greek value as a NATO southern flank and American forward operating base location. In light of the changing realities that have been shifted due to the demise of the Soviet Union, regional events, and the latest threats such as terrorism, this thesis also explores how MDCA have evolved over time. Focusing on US-Greek military cooperation, it maps the effects of a post-9/11 security landscape at: joint exercises, technological upgrades and defense capabilities that support Greece's capacity within NATO. In addition, the research addresses how diplomacy supports building and broadening of the MDCA, showing that high-level discussions have become essential in allowing for ongoing adaptability, creating space to cover new security threats. An important task is managing complex regional dynamics, especially rising tensions with Turkey and advancing peace and stability through cooperative frameworks. Also, it discusses the implications of the MDCA for regional stability and energy security in the Eastern Mediterranean, stressing Greece's geostrategic by rising competition among energy interests and matters pertaining to sea-based conflicts. It argues that the MDCA were not solely for military benefits but also to strengthen Greece's diplomatic position in international fora and during summits as being a credible stakeholder within NATO’s conciliating collective defense. This thesis concludes that the MDCA is not just a defense agreement but rather an all encompassing framework shrouding Greek-American relations, analyzing how interlinked diplomacy and military power are in shaping 21st century security threats. The conclusions underline the need for continued collaboration between Greece and America in replicating a stable and safe Eastern Mediterranean geography, with the MDCA there as one of many vital implements to this overarching objective.