3rd One. I recently read an article on this so I think its 3.
Answer:
The slave trade had devastating effects in Africa. Economic incentives for warlords and tribes to engage in the slave trade promoted an atmosphere of lawlessness and violence. Depopulation and a continuing fear of captivity made economic and agricultural development almost impossible throughout much of western Africa.
The Korean War was the second war in which the United Nations played a military role. The correct option among all the options given in the question is the second option. It was the toughest test for the United Nations after its inception. It was clear that the United Nations forces sent to Korea was dominated by American soldiers, but several other countries did participate in it.
