President Donald Trump's interest in a U.S. acquisition of Greenland, a semiautonomous territory of NATO ally Denmark, first became publicly known in 2019. Here's a timeline of events that led to a crisis between Washington and its European allies.

Denmark, Greenland and the United States are set to sign a deal on Greenland's ‌security on Tuesday, an agreement Denmark says will put Arctic security under NATO's watch rather than leaving it solely...