In a break with decades of US foreign policy and diplomatic protocol, President-elect Donald Trump spoke by phone December 2 with Taiwan President Tsai Ying-wen. The United States cut official diplomatic ties with Taiwan in 1979 after recognising the communist government in Beijing as the legitimate government of both China and the republic.
No US president (or president-elect) has had formal contact with a Taiwanese head of state since, though the two countries maintain an unofficial relationship. Mr Trump and President Tsai reportedly discussed the "close economic, political, and security ties" between the two countries. The call angered China.
But it is important. Throughout his campaign, Mr Trump spoke about marginalising NATO (the utility of the grouping appears to be a concern of NATO itself) and of allowing regional allied powers in various places around the world to have more autonomy in security (even to the extent of building nuclear weapons, which probably isn't a good idea).
This alarmed many US allies because they were already concerned with President Barack Obama's post-9/11 shift to a new strategic reality of creating a balance of power in particular regions. That balancing effort can look like US isolationism to the untrained eye. This strategic shift will continue forming throughout Mr Tump's administration because the civil service is planning for decades, not eight years - but that's beside the point.
The point is: America's allies are concerned about an acceleration of this strategic shift at a rate for which they aren't quite ready. All of them have their regional competitors and oppressors, which they fear will take advantage of a hasty US vacuum. They don't like those odds and are making preparations for this possibility. From Washington's perspective, that's not a good sign and it needs rectifying.
So a phone call to or from Taiwan is a signal to everyone else that the US won't abandon its commitments precisely because it chose to talk to the most controversial rival of the second-largest country on the planet. Allies will read the message loud and clear: If the US is willing to break protocol and risk annoying its near-peer China, then maybe they can be comfortable with a bit of rhetoric from the president-elect because the US isn't going anywhere.