Among the theories in international relations, I consider the theory of realism and idealism as the most important approach. Realism as it reflects real-life situations and events in the international community and provides clear explanation for the global conditions and events. It has the following assumptions that the international system is inherently anarchic, that sovereign nations are its primary actors, that all states within the system are unitary and rational actors, that states work on their own national interest, that they are always thinking of their own positive and the primary concern of all states is survival.

To ensure security in an anarchic world, states emphasizes an interest in accumulating power.
Survival through adopting ways to strengthen and develop their national defense and security.
States pursue power, they do this in the sense of trying to get more powerful positions and so that they can ensure their own self-preservation. Power in terms of material resources necessary to induce harm and to fight and win wars. There is a competition of power between states that becomes the strategy to accomplish something in the national interest.
One reason why I chose this theory of realism is the fact that it responds to and reflects global events. A state having non-objective and arbitrary law may lead to conflict of each state.

The state is the most important actor under realism. It is unitary and autonomous because it speaks and acts with one voice.