Definition: The home country of a colonial empire
When a country spreads beyond its immediate borders, the source or center of its power becomes the “metropole.” London, for example, was the metropole of the British Empire.
It’s from the word “metropolis,” which is Greek for “mother city.” Though, where metropolis has become generic to mean any large city, metropole carries a specific meaning.
Why I Looked It Up
In a book about the world in 1913:
In Algeria…empire meant the aggrandizement of the metropole, the spread of French civilization and influence…
Essentially, colonial Algeria was held up by the French as a celebration of French culture.