(A) ** when countries promise to help each other out
(B) Building up of a big army
(C) Wanting to control other countries and make them part of an empire
(D) the love of your country
EXPLANATIONS BELOW
Concept note-1: -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.
Concept note-2: -alliance, in international relations, a formal agreement between two or more states for mutual support in case of war.
Concept note-3: -First and foremost, having allies significantly increases the military power the United States can bring to bear on a given battlefield. During the Cold War, European forces were vital to maintaining something approximating a balance of power vis-à-vis Warsaw Pact forces.
Concept note-4: -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-5: -An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not explicit agreement has been worked out among them. Members of an alliance are called allies.