From the Introduction: "At a National Space Council meeting on June 18, 2018, President Donald Trump said, 'I am hereby directing the Department of Defense and Pentagon to immediately begin the process necessary to establish a space force as the sixth branch of the armed forces.' One of the purposes for creating a separate military service for space is to protect American interest in outer space. On February 19, 2019, the President signed Space Policy Directive-4 (SPD-4) directing the Secretary of Defense to submit a legislative proposal that would establish a U.S. Space Force, if enacted by Congress. In alignment with the President's National Security Strategy and the National Strategy for Space, the Space Force is intended to secure the vital interest of unfettered access to and freedom to operate in space while expanding American dominance in the space domain. Subsequently, on February 28, 2019, the Department of Defense (DOD) submitted a legislative proposal to Congress to create the U.S. Space Force."
CRS In Focus, IF11326
Congressional Research Service: https://crsreports.congress.gov/