Final answer:
Washington warned against foreign alliances to maintain political neutrality and avoid military entanglements, thus preserving U.S. security and independence.
Step-by-step explanation:
George Washington warned against foreign alliances primarily because he wanted to maintain political neutrality and avoid the United States being dragged into Europe's frequent and complex military entanglements.
Washington's farewell address emphasized the importance of the nation not getting entangled in permanent alliances that could lead to unnecessary involvement in foreign wars.
His overarching concern was to protect the fledgling nation's independence and security without getting embroiled in the conflicts and power struggles that were characteristic of European politics at the time.