Coming as it does at a time of growing great-power competition, this narrowing definition of American interests will likely hasten a return to the instability and clashes of previous eras. The weakness at the core of the democratic world and the shedding by the United States of global responsibilities have already encouraged a more aggressive revisionism by the dissatisfied powers. That, in turn, has further sapped the democratic world’s confidence and willingness to resist. History suggests that this is a downward spiral from which it will be difficult to recover, absent a rather dramatic shift of course by the United States.

That shift may come too late. It was in the 1920s, not the 1930s, that the democratic powers made the most important and ultimately fatal decisions. Americans’ disillusionment after World War I led them to reject playing a strategic role in preserving the peace in Europe and Asia, even though America was the only nation powerful enough to play that role. The withdrawal of the United States helped undermine the will of Britain and France and encouraged Germany in Europe and Japan in Asia to take increasingly aggressive actions to achieve regional dominance. Most Americans were convinced that nothing that happened in Europe or Asia could affect their security. It took World War II to convince them that was a mistake. The “return to normalcy” of the 1920 election seemed safe and innocent at the time, but the essentially selfish policies pursued by the world’s strongest power in the following decade helped set the stage for the calamities of the 1930s. By the time the crises began to erupt, it was already too late to avoid paying the high price of global conflict.

In such times, it has always been tempting to believe that geopolitical competition can be solved through efforts at cooperation and accommodation. The idea, recently proposed by Niall Ferguson, that the world can be ruled jointly by the United States, Russia, and China is not a new one. Such condominiums have been proposed and attempted in every era when the dominant power or powers in the international system sought to fend off challenges from the dissatisfied revisionist powers. It has rarely worked. Revisionist great powers are not easy to satisfy short of complete capitulation. Their sphere of influence is never quite large enough to satisfy their pride or their expanding need for security. In fact, their very expansion creates insecurity, by frightening neighbors and leading them to band together against the rising power. The satiated power that Otto von Bismarck spoke of is rare. The German leaders who succeeded him were not satisfied even with being the strongest power in Europe. In their efforts to grow still stronger, they produced coalitions against them, making their fear of “encirclement” a self-fulfilling prophecy.

Eoin Treacy's view

US isolationism in one form under Obama and taking another form under Trump represents a change to the global geopolitical balance. It leaves an opening for increasing “assertiveness” from Russia, China and their proxies. That represents a medium-term risk premium for markets but is unlikely to represent a problem in the short term.