In 1919, Within the finishing of First World War, International Relations established as a dicipline and put many newnesses in the world. After First World War, people who saw the bad subsequents of war, didn’t want to live such a bad thing once again. International Relations Dicipline didn’t also become indifferent this situation and ıt became to one of the acceptors of this subject with a great debate. This was Idealism-Realism Debate. It tried to both remain the peace, to prevent the war and to brought in the identity to own dicipline.                 Idealists who dated back to Stoicism theirselves, brought forward assumptions that were logical ın their own era to prevent the war, to ensure the peace and to resolve to problems.  These were International Law that had hard sancions, everybody accepted and obeyed it, International Organization that included every states without making discrimination and Disarmament ınternationally. According to them, in such a situation, ensuring the peace  will be easier and possible.                 Realists who dated back to Peleponnesian War theirselves, on the contrary to Idealists, maintained that war couldn’t prevent, was unavoidable and necessary because of human nature and They criticized the Idealists.                 This article will examine The, İdealism , İdealists, their assumptions, Realism, its assumptions, Idealism-Realism Debate and Idealists’ assumptions that brought forward to prevent the war, to ensure the peace and to resolve the problems.