Final answer:
The phrase 'To the shores of Tripoli' signifies the U.S. military action against Barbary pirates during the First Barbary War and is commemorated in the Marines' Hymn.
Step-by-step explanation:
The phrase To the shores of Tripoli refers to the early 19th-century conflict between the United States and the Barbary pirates, based in the Tripolitanian city of Tripoli, which is now the capital of Libya. Specifically, it signifies the U.S. naval expedition sent to the Barbary Coast during the First Barbary War (1801-1805) to combat piracy and free American hostages. This historical event is notably commemorated in the first line of the Marines' Hymn and symbolizes the United States military's readiness to protect American interests even in distant lands across the seas.