American global power was not achieved through deliberate imperialist foreign policy.

Evidence

Whatever the causes for American ascendancy to world power, the deliberate pursuit of a foreign policy leading to it or any claim to global rule are not among them. And the same is probably true for the country’s recent and still tentative steps in the direction of imperialist power politics for which its form of government is less fitted than that of any other country. — Hannah Arendt, The Origins of Totalitarianism, 31