If Donald Trump tries to implement his worldview, he could ignite a new world crisis. World crises are rare. They occur when a fault-line opens up in the international system that generates enormous instability and unleashes powerful opposing forces with no means of reconciling them. 

The last world crisis occurred in the late 1940s with the breakdown of the post-war settlement, Soviet expansionism, containment, and the advent of the Cold War. 

Before that, the emergence of Nazi Germany destroyed the equilibrium in Europe and paved the path for the World War II.

This crisis is simple enough to understand. The United States could withdraw from its role as the leader of a liberal international order. 

The order would then collapse and other countries would scramble to respond.