A Reuters article suggested last week that the United States is considering withdrawing as many as 4,000 troops from South Korea if Seoul does not pay more money to maintain the U.S. deployment there. The Pentagon denied the report, which appeared to echo other reports that President Trump demanded greater contributions from South Korea and Japan to support the U.S. military presence in those countries.

Is the 66-year-old alliance with South Korea in “deep trouble,” as one Washington Post editorial suggests? A Korea Times headline said it bluntly: “Put alliance before money.”

Debates over burden sharing — how the United States and its allies split the costs of providing security — date to the beginning of the Cold War, but Trump’s moves could have major consequences for U.S. alliance relationships. Here’s what you need to know.