Abstract
Under the check and balance political system of the United States, the foreign-policy-making power is shared by Congress and the president, which results in the unique"bipolar diplomacy"power structure in the field of forein affairs. This paper first tends to explain the reason for such a bipolar structure, and then with the analysis of the strggle and conflicts about war power between these two branches after the Second World War. it reviews the power shift of Congress as a relatively independent institution and its influence upon the foreign policy of the states.

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