Idealism in international relations usually refers to the school of thought personified in American diplomatic history by Woodrow Wilson, such that it is sometimes referred to as Wilsonianism. Idealism holds that a state should make its internal political philosophy the goal of its foreign policy. For example, an idealist might believe that ending poverty at home should be coupled with tackling poverty abroad. Wilson's idealism was a precursor to liberal international relations theory, which would arise amongst the "institution-builders" after World War II.

Idealism is also marked by the prominent role played by international law and international organizations in its conception of policy formation. One of the most well-known tenets of modern idealist thinking is democratic peace theory, which holds that states with similar modes of democratic governance do not fight one another. Wilson's idealistic thought was embodied in his Fourteen points speech, and in the creation of the League of Nations.

Idealism transcends the left-right political spectrum. Idealists can include both human rights campaigners (traditionally, but not always, associated with the left) and American neoconservatism which is usually associated with the right.

Idealism may find itself in opposition to Realism, a worldview which argues that a nation's national interest is more important than ethical or moral considerations.

From : en.wikipedia.org