It's unclear how the issue of ownership of the Panama Canal became a talking point for President-elect Donald Trump this week, but the question has a long political history.

In recent days the president-elect has called for asserting U.S. control over the Panama Canal and Greenland, showing that his “America First” philosophy has an expansionist dimension.

At first, he joked about Canada being an additional US state. Since, he has threatened to take back control of the Panama Canal. He also reiterated a desire from his first term to own the autonomous Danish territory of Greenland, which is not for sale.