Question

Why couldn't European countries maintain their overseas colonies after World War II?

The European countries were economically ruined by war.
The world was bipolar.
Their leases could not be renewed.
The Europeans wanted to colonize Antarctica instead.

Answer 1

The European countries were economically ruined by war.

Many nations suffered terrible losses during WW2, Germany especially, and a number of plans were drawn up later to help get them back on their feet.

The other reasons don't make much sense. The world having a north and south pole had as much impact as the sky being blue, the colonies didn't necessarily have leases, and the only colonies in Antarctica were those for penguins.