By casting doubt on the world order, U.S. President Donald Trump risks dragging the globe back into an era where great powers impose their imperial will on the weak, analysts warn.

Russia wants Ukraine, China demands Taiwan and now the U.S. president seems to be following suit, whether by coveting Canada as the "51st U.S. state," insisting "we've got to have" Greenland or kicking Chinese interests out of the Panama Canal.

Where the United States once defended state sovereignty and international law, Trump's disregard for his neighbors' borders and expansionist ambitions mark a return to the days when the world was carved up into spheres of influence.