Idealists are actually Liberals. Most of their claims are synonymous with the Liberals. However, there's one difference. Liberals, the likes of Immanuel Kant, believe that humans are naturally peaceful. Ideals, on the other hand, the likes of Woodrow Wilson, believe that peace must be constructed through world institutions. This belief of ideals led to the formation of League of Nations after the Great War. You can read more about it in John Baylis' book "Globalisation of World Politics".