From the Document: "Kuwait has been pivotal to the decades- long U.S. effort to secure the Persian Gulf region because of its consistent cooperation with U.S. military operations in the region and its key location in the northern Gulf. Kuwait and the United States have a formal Defense Cooperation Agreement (DCA), under which the United States maintains over 13,000 military personnel in country and prepositioned military equipment in Kuwait to project power in the region. Only Germany, Japan, and South Korea host more U.S. troops than does Kuwait, which hosts the operational command center for U.S.- led Operation Inherent Resolve (OIR) that has combatted the Islamic State."
CRS Report for Congress, RS21513
Congressional Research Service: https://crsreports.congress.gov/