The phrase "manifest destiny," was coined by New York journalist John O'Sullivan in 1845, when he wrote that "it was the nation's manifest destiny to overspread and to possess the whole of the continent which Providence has given us for the development of the great experiment of liberty and federated self-government entrusted to us." That same year on December 2, U.S. President James Polk announced to Congress that the Monroe Doctrine should be strictly enforced and that the United States should aggressively expand into the West.
The "Manifest Destiny" the US belief that it was their right and destiny to rule the lands of the Americas. An expansionist attitude, aggression used if required.
With this in mind, how possibly could an American attack Britain on it's expansionist and imperialist attitude?
No blame lies with America, it was a product of its age.