Why did mother countries build colonies?

Colonies were a way for the mother country to engage in the practice of mercantilism, or increasing their power by creating a source for exports and raw materials. ... During the Age of Imperialism in the late 19th century, many colonies existed as a result of competition between world powers.

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the triple alliance. germany and austria-hungary were already allies by 1879 when, worried about a threat from russia, they formed the dual alliance. italy joined the group in 1882. there was a concern about a possible attack from france and the alliance needed powerful friends to defend it.