Imperialism is derived from the Latin word imperium which means supreme power. Imperialism refers to a situation where a powerful country establishes its control over another country. It could be because of
Political pressure
Infiltration
Annexation
This controlled country or the conquered country will be referred to as the colony of the controlling country.
These colonies were exploited for:
Raw materials - to run the factories of the colonisers
Cheap labour - The population of the colonised country could be forced to work for cheap wages or sometimes no wages.
Agricultural lands - The agricultural lands of the colonies to grow commercial crops like cotton, indigo or tobacco.
Trading ports - Colonisers could use the colonies as trading ports.