The American empire dates from just after the end of the Second World War

American historian Howard Zinn was a Communist fellow traveller and exposed as a KGB agent, but these words of his on the Allied victory in 1945 are accurate. 

"The victors were the Soviet Union and the United States (also England, France and Nationalist China, but they were weak). Both these countries now went to work – without swastikas, goose-stepping, or officially declared racism, but under the cover of 'socialism' on the one side, and 'democracy' on the other, to carve out their own empires of influence. They proceeded to share and contest with one another the domination of the world, to build military machines far greater than the Fascist countries had built, to control the destinies of more countries than Hitler, Mussolini, and Japan had been able to. They also acted to control their own populations, each country with its own techniques – crude in the Soviet Union, sophisticated in the United States – to make their rule secure."

England, France and Nationalist China's victories were, of course, Pyrrhic. Since 1991 only the United States' empire remained but now, as was inevitable, it is being challenged.