Britian’s Royal Navy kept the worlds oceans safe for trade for several centuries. Early in the 20th century they became obsessed with Battleships to safeguard against the Germans, French, Japanese, and U.S. Navy.
The period between the world wars the British and everyone else couldn’t afford a Naval arms race. Especially an arms race between the USA and Britain! The Washington naval arms treaty was useful until Japan and Germany went nuts with militarism. We know what happened next.
At the end of WW2 the USA by default safeguarded the world’s trade routes.