I know during the Revolutionary War it was a pretty big feat to beat the leading superpower at the time but when did the U.S. really became so influential? Was it before or after Hiroshima?
The US economy outpaced that of the French and German Empires in the 1870s, and overtook the British Empire in 1916. This is clearly a major change in America’s position on the global stage, and coincided with industrial development and successful involvement in two wars - the Spanish-American War, in which the United States gained the territories of the Philippines and Puerto Rico, and World War I, which the US emerged from with its territory intact, unliked the war-ravaged France, Belgium, and Germany.
Of course, ‘superpower’ has a different connotation than that of ‘great power’, and it was not until the end of World War II that America claimed this title. With Germany destroyed and divided by war, the great toll on the British Isles and movements for independence in the British colonial possessions, and the end of Japanese imperial ambitions, America was largely unmatched by any world power save the USSR. The foundation of NATO and the Warsaw Pact solidified this alignment, the ‘squaring-off’, if you will, which we see in many presentations of the Cold War as a conflict between the superpowers of the USA and the USSR.