For 150 years, the US avoided formal alliances. It occasionally went to war -- fighting the War of 1812, the Spanish-American War, and World War I -- but did so without entangling itself in promises to other countries. Then, after World War II, it abruptly changed course, and began to build a network of alliances unlike anything that had come before.

Over the next few decades, the US used those alliances to keep countries around the world close, and to fight Soviet expansion, by making a promise that it would go to war if any of its allies were ever attacked. After the Soviet Union fell, the initial purpose of those alliances was gone, but the US recommitted to them, signaling again and again that the central promise of those relationships was still in effect. It kept doing so for the next 25 years.

Then the US elected a leader who took America’s global relationships in a new direction. President Trump was skeptical that America’s network of alliances was still beneficial to the US. He began to distance the US from those alliances, raising doubts about whether America would actually follow through on the promise at the core of them if provoked. Some allies moved closer to Russia or China, both of whom had attempted to undermine America’s alliances.

Today, the future of those alliances is on the ballot in the US. One of the major presidential candidates in the 2020 election wants to return the US to its former status with its allies; the other finds its decades-old alliances costly and cumbersome. The world is waiting to see which vision Americans prefer.