Answer:
The Monroe Doctrine
Explanation:
The doctrine threatens European nations by not allow more colonization and monarchs rule in the Western Hemisphere. The Monroe Doctrine was a foreign policy issued in 1823 under the presidency of James Monroe.
President James Monroe states that America has never interfered in foreign matters before. When the rights of the Americas jeopard, then it became necessary to get involved in the issue. The United States will not allow colonization and monarchs rule because it will further lead to the establishment of a colony in America.
Economically:
As imperial states began controlling the economy of the colonized territory, interests for the welfare of the colonized peoples had little influence in defining their economic policies. ... Thus, imperialism had a highly negative effect on the economic growth of colonized nations.
Politically:
The long term effects of imperialism on the colonized people are political changes such as changing the government reflect upon European traditions, economic changes that made colonies create resources for factories, and cultural changes that made people convert their religion.
Socially:
According to other authors, the social impact of colonialism depended on the number settlers of European origin, colonially-induced labor migration and the level of colonial investment in the health and education sector. Related to that were different practices of ethnic and/or religious discrimination or privileges.
I'm pretty sure (1.) is A, and I know for a fact that (3.) is D because slavery was a regular practice between quarreling tribes. I have no clue what (2.) is. Best of luck.