The United States is an expansionist empire
To be fair, the United States is an expansionist empire (and has been such from the beginning):
Renounce the mother country, expel and exterminate the indigenes, expand and fill the continent. The US-Phillipine War (1899 to 1902), and later the Vietnam War ( 1955 to 1975), demonstrate how the Westward Expansion would have expanded to conquer the entire planet, had it the the power to do so.
Still, the American Empire has done surprisingly more for humanity than previous empires, as David Brin points out:
"Pax Americana was horribly expensive, but more benign than most empires. The Vietnam War was cosmically wasteful and tragic, as has been the Arms Race, but on the whole, a larger fraction of the world’s people had a chance to spend less time protecting themselves than in any prior era."
