To America's allies and fellow treaty signatories from Europe to South America , Trump's approach "stands in stark contrast to the dominant strain of internationalism that has marked U.S. foreign policy since the days of Franklin Roosevelt and Harry Truman," Steven Patrick of the Council on Foreign Relations wrote in November. (Less than two months later, House lawmakers introduced a UN membership-ending bill called the " American Sovereignty Restoration Act of 2017 ," among the first submitted to the 115th Congress in early January.) Since the end of World War II, America's consistency had been something that "long reassured partners and allies," said Patrick.

Defense Secretary James Mattis wasted little time in his first days on the job, traveling for four days to visit with counterparts from Japan and South Korea, allies with a careful eye on nuclear-armed North Korea. They are among the most recent to be added to America's list of collective defense arrangements, pictured below. Not all have kept their original members—NATO expanded, Rio signatories declined—but all remain active, according to the State Department.

Power in alliances

The nations that are allied with the U.S. have 6 million people in total military manpower and account for more than 60 percent of global defense spending (more than $1 trillion), according to a 2017 report from the conservative think tank Heritage Foundation. See the map below for troop counts of each U.S. ally listed under the State Department’s collective defense agreements.

Size of U.S. allies’ militaries