mother country 
noun
A country in relation to its colonies: Australia sent the flower of its youth to defend the mother country’s interests...
- The relationship between the mother country and the remaining colonies, the Netherlands Antilles and Surinam, was to be put on an equal footing.
- My English friend, on his maiden voyage to the States, had stumbled upon one of those little linguistic divergences between the colonies and the mother country.
- There are fewer opportunities to trade with the mother country in a far colony.