Unilateralism

Unilateralism is a policy of making a decision internally to a country, without serious diplomatic input from other countries, and then requiring or imposing it on others. The United States is usually considered to be the most capable of exercising unilateral policies, though China also does so and sometimes Russia and India in their spheres of influence. The usual justifications for unilateral acts are national security and (if this fails) national sovereignty.

Multilateralism is defined by contrast to unilateralism and refers to those actions and forums where decisions are not pre-made by the most powerful party at the table.