United States European Command: Overview and Key Issues [Updated February 13, 2020] [open pdf - 446KB]
From the History: "The collapse of the Soviet Union led to a withdrawal of the bulk of forward-deployed U.S. troops in the European theater. Decisions to do so were arguably based on a number of strategic assumptions held by successive administrations after the end of the Cold War, including that:  Europe could be stable, whole, and free;  Russia could be a constructive partner in the Euro-Atlantic security architecture; and  particularly prior to September 11, 2001, threats posed by terrorism and migration from the Middle East/North Africa region were limited. EUCOM [United States European Command] subsequently focused its activities on non-warfighting missions, including building the security capacity and capability of former Soviet bloc states, prosecuting 'crisis management' operations in the Balkans, and logistically supporting other combatant commands (by providing, in particular, critical medical evacuation facilities at Landstuhl), including U.S. Central Command (CENTCOM) and U.S. Africa Command (AFRICOM). Over the past 25 years, decisions regarding U.S. basing and posture in the European theater have largely reflected these assumptions. The bulk of U.S. forces in Europe have been withdrawn and many bases and outposts were either consolidated or closed. However, two Brigade Combat Teams (BCTs) were retained (in Italy and Germany) as were some naval bases, particularly those along NATO's southern flank, and a number of Air Force bases that were deemed critical for supporting operations in the Middle East, Africa and Europe."
CRS In Focus, IF11130
Congressional Research Service: https://crsreports.congress.gov/