The phrase 'Pax Americana' can therefore be used to describe an era without major war post-1945, overseen by the stabilising force and military might of the United States.
The United States entered the war late, brought its forces home quickly afterwards and refused to help enforce a peace its president helped design due to the US Congress rejecting membership of the League of Nations.
When the war began in 1939 there were several powers contesting for global leadership, but the United States was not among them.
In contrast, by 1945 the United States had shaken off the effects of the Great Depression, the global economic collapse of the 1930s, and was relatively untouched by the war.
The United States took several lessons from the Second World War, the most important of which was that it had to be involved in managing global security in order to protect its own security.
Because international relations as a system is anarchical, with no ruler, powerful states tend to make other states feel insecure by default.
To monitor the situation, the United States chose to be involved globally, designing the international frameworks for commerce and governance at conferences it convened in Bretton Woods and San Francisco, both in America, and joining the United Nations which was headquartered in New York City.
Although the bulk of its forces were demobilised at the war's end, the United States maintained the network of bases it had built during the war and retained a substantial…