Donald Trump says the U.S. needs control of Greenland and the Panama Canal "for national security." Here's why both places are so important.

But Trump’s concerns are also heavily influenced by something he often does not acknowledge: climate change and its growing influence on national security.Start the day smarter. Get all the news you need in your inbox each morning.

Authorities of Panama and Greenland have repeatedly said they won't hand over any territory to Trump, with Panama's president declaring that the canal "is going to stay in our hands forever," and Denmark's prime minister insisting "Greenland is not for sale."