Imperialism - when it occurred and why

Why: To enlarge power of a Nation or group or leader. When: long ago, mid third millennium BC

Explanation:

Imperialism is a policy or ideology of extending a country's rule over foreign nations, often by military force or by gaining political and economic control of other areas.[2] Imperialism has been common throughout recorded history, the earliest examples dating from the mid-third millennium BC. In recent times (since at least the 1870s), it has often been considered morally reprehensible and prohibited by international law. As a result, propagandists operating internationally may use the term to denounce an opponent's foreign policy.[3]

Not gonna take credit for this cuz it's from Wikipedia

In the age of the new imperialism that began in the 1870s

Various motives prompt empires to seek their rule over other countries or territories.

These include economic, exploratory, ethnocentric, political and religious motives.

b europeans take corn to africa. corn becomes an important crop there.