America had invaded other nations, often, clandestinely. One of the earliest operation took place during the ‘First Barbary War’.
When Thomas Jefferson became President in 1801, he refused to pay tribute and sent a United States Naval fleet to the Mediterranean.
The fleet bombarded various fortified pirate cities in Libya, Tunisia, and Algeria. The most famous event of the war occurred in April and May of 1805 with the Battle of Derma.
General William Eaton and First Lieutenant Presley O’Bannon led a force of eight Marines and 500 mercenaries from Egypt across the desert to the city of Derma.
Americans used people from Egypt to fight their war. This method would be further refined to use the nationals of whatever nation they were attempting to conquer.