Theories of International Relations have been categorized or classified by different writers or scholars. Among these, the classification as realism, liberalism and Marxism are very common. Since some concepts are being used to define these concepts, some others are using different identification for the same ones. For example, conservatism or Machiavelism as well as Hobbesianism could be used instead of realism. Similarly, instead of liberalism some scholars are using pluralism, Kantianalism or Grotianalism. The same conceptual difference would be for Marxism since some writers are using radicalism or globalism to define the same thing.