This work is the first of two the authors are writing on the unique and paradoxical nature of American foreign policy - its conflicting isolationist and messianic impulses which lead it to pursue an expansionist role in world affairs while advocating democratic goals at home and abroad. The roots of this paradox, the work argues, lie in Thomas Jefferson's political philosophy and statecraft which has had a major influence on the American worldview, and continues to shape our foreign policy in profound ways.