(A) ** alliance
(B) nationalism
(C) isolationism
(D) friendship
EXPLANATIONS BELOW
Concept note-1: -Alliances are formal agreements between two or more nations. In national defense, they’re promises that each nation will support the other, particularly during war.
Concept note-2: -The obvious motivation in states engaging in military alliances is to protect themselves against threats from other countries. However, states have also entered into alliances to improve ties with a particular nation or to manage conflict with a particular nation.
Concept note-3: -In international relations, an alliance is a group of countries that come together to promote their common security interests. In many cases, alliances promise military support if one member is threatened, a formal commitment known as mutual security.