As a European whose formal education on American history consisted of the World Wars & Revolution, I was led to believe the American Republic was originally conceived as almost a rejection of imperialism in general. I now know this to be not entirely accurate, however find the subject of American imperialism & neo-colonialism fascinating, although I don't know nearly enough about it.
Do you think there was a particular piece of legislation/war that cemented America's new role as an empire. I appreciate this depends on ones definition of 'empire'. I'd say a nation willing and able to consistently interfere in the issues of other nations - to its own benefit, with a large sphere of influence and the overseas territories that entails. But I really don't know masses about this area; you're the experts!
Additional question; is it fair to say private commerical interests were always the primary drivers of American expansion & latter interference in foreign nations e.g. changing regimes, installing loyal governments etc etc.
Thanks!
If you want to learn when and why the USA embraced the idea of empire and imperialism, you need to go further back than the 19th century. The original Thirteen Colonies declared independence in large part out of a desire to pursue empire and colonialism rather than to reject it. The republican experiment undertaken in 1776 was predicated on the idea that the nation would be an empire.
I appreciate this depends on ones definition of 'empire'. I'd say a nation willing and able to consistently interfere in the issues of other nations - to its own benefit
The colonies were founded on a basis of interference with their neighboring nations: the Native American tribes. England and later Great Britain had relatively little to do with the territorial expansion of the American Colonies before 1754 compared to the colonial actors on continent. They consistently and continually worked to dispossess the indigenous peoples or otherwise subjugate them to colonial authority, to mixed success. Some colonies, like Massachusetts and Virginia, were able to carve up indigenous land far inland from the Atlantic coast, while others were largely confined to within 100 miles of the coast. Native peoples largely controlled access to the interior and, though they successfully dispossessed some groups like the Narragansetts or the Powhatans, they were less successful with dozens of other tribes who successfully resisted English incursions and even dictated the terms of encounter with them.
The tide began to turn following the Seven Years War, when Britain secured an illusory claim to all of North America east of the Mississippi River. I say illusory because, even though the British and the colonies claimed this land, it remained firmly in indigenous hands. The Seven Years War itself was predicated on empire-building for the purposes of enriching the colonies, not the metropole back in Europe. A young George Washington started the conflict when he led a small groups of Virginia soldiers to lay claim to Ohio, then in the hands of a loose confederacy of indigenous tribes allied to the French. The British tried to lay claim to Ohio and the trans-Appalachian west following the end of the Seven Years War, but two uprisings led by native leaders named Pontiac and Neolin in 1763 prompted the British to firmly restrict colonial settlement west of the Appalachian Mountains in order to keep the peace.
The American Colonies were royally peeved by these restrictions, as they saw the indigenous lands as their natural birthright and chafed under the restrictions to extend the colonial enterprise. This and many other factors contributed to the onset of the American Revolution, severing political ties with the British Empire in order to start a new "infant empire," as George Washington described it in 1786. The new empire immediately sought huge concessions of land from the indigenous tribes previously allied with the British Empire after the end of the war, wasting no time to expand the empire and make the illusory claims represented on the map a reality. The endeavor got off to a rocky start until 1815, when Britain no longer aided the indigenous peoples in hindering the westward march of American empire.
The remainder of the 18th and most of the 19th century was spent extending this empire and subjugating and dispossessing the indigenous nations occupying and living on the land as they had for centuries prior. What is often confused as the emergence of an American empire at the end of the 19th century was actually the extension of a pre-existing empire that began well before 1776 and continues to this day.
Edit: added some more sources for further reading
Sources:
Carroll Smith-Rosenburg - This Violent Empire: The Birth of an American National Identity
James D. Drake - The Nation's Nature: How Continental Presumptions Gave Rise to the United States of America
Jill Lepore - The Name of War: King Philip's War and the Origins of American Identity
Peter Silver - Our Savage Neighbors: How Indian War Transformed Early America
Richard White - The Middle Ground: Indians, Empires, and Republics in the Great Lakes Region, 1650-1815
Richard H. Immerman - Empire for Liberty: A History of American Imperialism from Benjamin Franklin to Paul Wolfowitz
Eliga Gould - Among the Powers of the Earth: The American Revolution and the Making of a New World Empire