Why was the end of the 19th century know as the "Age of Imperialism"? A African countries aggressively expanded their empires in United States
B European countries aggressively expanded their empires in Asia and Europe
C African countries aggressively expanded their empires in Asia and Africa
D European countries aggressively expanded their empires in Asia and Africa

It came into use after 1850. It was a new kind of European expansion which was not marked by widespread settlement. Its objective was to control territories for political and economic reasons and for national prestige. The late 19th century is often called the Age of Imperialism

the exclusive possession or control of the supply or trade in a commodity or service.

the missile gap was the cold war term used in the us for the perceived superiority of the number and power of the ussr's missiles in comparison with its own (a lack of military parity).