Abstract: E.H. Carr is the founding father of realism in international relations, and his magnum opus-The 20 Year's Crisis (1919~1939): An Introduction to the Study of International Relations-is a classic masterpiece of realism in international relations, in which the author E. H. Carr applied the viewpoints of Marxism to criticizing the idealism in international relations during the two world wars. E.H. Carr's research began with the realism in traditional politics, and he then analyzed Marxism in the light of the differences between research objective and research process and replaced Marx's theory of class struggle with ‘harmony of class interest’. He thought that Marx simply materialized Hegel's concept conflict, insisting that economic force was actually using political force to confuse the relationship of the two as deciding factor or being decided, using the consistency of relative evaluation on law to confuse the fact that the ultimate purpose of realism was to return to capitalist system and distinguishing Russian Revolution and Soviet policies by ideology to negate Marxism.