What was the relationship between American imperialistic desires and the closing of the frontier?

Some historians have argued that the closing of the American frontier, which occurred with the census of 1890, actually promoted imperialism. Historian Frederick Jackson Turner, speaking in 1893, argued that the existence of a frontier, what he called "free land" in the West had always been important in promoting democracy in the United States. This view, while widely discredited by modern historians, expressed a belief among many late nineteenth-century Americans that expansion was essential to maintaining America's economic and cultural growth. With no more frontier left on the North American continent, this interpretation goes, Americans began to look elsewhere, both in the Caribbean and in the Pacific, to satisfy their ambitions. Many imperialists, like Theodore Roosevelt in his famous speech, "The Strenuous Life," were able to cast imperialism as a challenge that his generation of Americans could rise to after the struggle to subjugate the Native Americans in the West (which was not, whatever Jackson Turner says, "free land). Having conquered the West, Roosevelt argued, it was time for American men to rise to "one of the great tasks set modern civilization": to spread American civilization and power overseas. On the other hand, it is important to remember that many Americans had been advocating imperialism in a number of areas--the conquest of the Caribbean and Central America, for instances, as well as gaining control over Hawai'i--for decades before the Census Bureau declared the frontier "closed". So if the closure of the frontier was a factor encouraging imperialism, it was one of many.