Aspects of international relations have been studied as early as the time of the ancient Greek historian Thucydides. As a separate and definable discipline, however, it dates from the early 20th cent., when the first organized efforts were made to find alternatives to wars in nation-state international behavior. Two schools of thought quickly developed. One looks to strengthened international law and international organizations to preserve peace; the other emphasizes that nations will always use their power to achieve goals and sees the key to peace in a among competing states.