In the 1920s, the American economy prospered. A new employment and industry was born by the First World War, and members of society such as women became increasingly deep in society, its role was being redefined. America is becoming an industry leader in the world. To protect American consumers from European imports and to encourage American products, the US government imposes high tariffs. In short, America no longer wants to keep in touch with Europe.
Geography plays an important role in promoting American isolationism. From the center of the United States, other parts of the world look distant. Since the 19th century, when the United States spread its borders to the Pacific and Mexico, that country has been buffered by its pure land from the outside world. Canada was originally a small settlement and Mexico was hit by internal dissent and was not threatened. The place is even smiling at the United States. Its abundant resources and growing domestic market has historically restricted economic dependence on other countries of the world. Even after the United States became the most powerful economy in the world in 1945, most of its trade and investment was within its own borders. Adding two huge seas on both sides, the United States, unlike most other countries in the world, is not afraid of most of its history by foreign invaders.
American isolationism legalizes the Treaty of Versailles. If one of the key supporters (and one of the emerging world powers) refuses to join, why does other society invest in the agreement? Many observers admit the refusal of domestic politics behind the treaty, but this only deepens the awareness that the United States has long been considered an untrusted partner. If America is hitchhiking, why is another person holding his hand? In the decade after the First World War, the American behavior encouraged other powerful officials, in particular Japan, Germany, and the newly formed Soviet unilateralism.
I dare say that the second characteristic of this new post-Cold War world is the revival of America's isolationism. I am wrong. The fact proves that the new norm of the United States is not the withdrawal after World War I but participation after the Second World War. In the 1990's, Pat Buchanan did isolationism in the 1930's. He eventually took Palm Beach. Finally, I propose that the third feature of this new monopolar world is an increase rather than a reduction of the threat of war. In the past, this was a powerhouse that was a major threat to global peace, so this will constitute a revolution in international relations.