冷戰使得聯合國的集體安全制度無法實現。秘書長哈瑪紹代以「維和行動」，但其目的只是消極的防止衝突擴大或恢復衝突前的狀態，並不求化解衝突。冷戰結束後，安理會在大國合作下，積極化解衝突，締造和平，發動所謂的第二代維和行動。有時為了迫使衝突各造遵守解決衝突的方案，安理會動用憲章第七章下的權力，採取強制執行行動，因而形成所謂的第三代維和行動。第二代和第三代維和行動已成為聯合國維持國際和平與安全的新趨勢。

　　　　　The Cold War prevented the UN from realizing its collective security system. UN Secretary-General Dag Hammerskjold replaced it with peacekeeping operations which in principle seek to freeze but not resolve conflicts. The end of the Cold War enabled the Security Council to carry out its responsibility for maintaining international peace and security. It has sought to resolve conflicts and build peace, thereby engaging in so-called second generation peacekeeping operations. The Council has sometimes resorted to enforcement actions under Chapter 7 of the UN Charter, in order to force the parties of a conflict to accept and abide by peace-making arrangements, thereby engaging in third generation peacekeeping operations. The later two kinds of operations have become the prevailing mode of the UN for maintaining international peace and security.