Since the start of Donald Trump’s run for the U.S. presidency in 2015, he has been critical of the amount of money U.S. allies contribute to their own defense.

Now, the Trump administration is demanding that Japan and South Korea pay more for hosting U.S. troops stationed in those countries.

The media also reported that U.S. military leadership in South Korea discussed the possibility of withdrawing up to 4,000 troops from South Korea if it does not increase its contributions. The Pentagon has since denied having such plans.

We have each studied overseas deployments of U.S. military personnel for nearly a decade and have recently come together to research the costs and benefits of such deployments.