“I believe strictly in the Monroe Doctrine, in our Constitution and in the laws of God,” one American religious leader declared in 1923. That same year, 10 million American schoolchildren were subjected to a centennial recitation of President James Monroe’s famous doctrine in class.

“The American continents, by the free and independent condition which they have assumed and maintain, are henceforth not to be considered as subjects for future colonization by any European powers,” Monroe said in December 1823. For generations thereafter, that statement was a cardinal principle of US policy. It fused America’s founding ethos of anti-imperialism to the fierce nationalism and outrageous ambition that ultimately allowed the country to surpass every empire on Earth. It even became central to the America’s understanding of itself.