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.

President-elect Donald Trump has once again repeated his desires for U.S. territorial expansion. In a message delivered on Christmas Day, Trump took aim at the Panama Canal and Greenland, while also addressing Canadian Prime Minister Justin Trudeau directly.