American isolationism is an ambiguous concept. The United States has never been isolationist with regard to commerce. Our merchant vessels roamed the seven seas from the first days of independence. Nor has the United States been isolationist with regard to culture. Our writers, artists, scholars, missionaries, and tourists have ever wandered eagerly about the planet. But through most of its history, the republic has been isolationist with regard to foreign policy. From the start, Americans sought to safeguard their daring new adventure in government by shunning foreign entanglements and quarrels. George Washington admonished his countrymen to "steer clear of permanent alliances," and Thomas Jefferson warned them against "entangling alliances."
Only a direct threat to national security could justify entry into foreign wars. The military domination of Europe by a single power has always been considered such a threat. "It cannot be to our interest," Jefferson observed when Napoleon bestrode the continent, "that all Europe should be reduced to a single monarchy." America would be forever in danger, he said, should "the whole force of Europe [be] wielded by a single hand." But between Napoleon and the kaiser, no such threat arose, and Americans became settled in their determination to avoid ensnarement in the corrupt and corrupting world. Isolationism, in this political sense, was national policy.
Then World War I revived the Jeffersonian warning. Once again, as in the time of Napoleon, the force of Europe might have been wielded by a single hand. A balance of power in Europe served