Pre-emption and unilateralism are the two most frequently used terms against President George W. Bush's foreign policy in the current presidential election campaign. Sen. John Kerry, the Democrat Party's presidential nominee, accuses Bush of breaking with an established tradition of American foreign policy. Kerry says the US should use force only after it is attacked, and then, only in conjunction with allies, and endorsement by the United Nations. Unilateralism and pre-emption, Kerry asserts, are alien to American traditions. But are they?Both the kind of foreign policy that Kerry offers and the one practiced by Bush after Sept.11 , 2001 have deep roots in American history. When the United States emerged as an independent nation in the 18th century, virtually the entire world was dominated by European colonial powers. The chief concern of early American leaders was to steer clear of European rivalries, and avoid trouble in their own backyard.