With a POD after 1803, your challenge is for the USA to cover North and South America by 2000.
There were the stirrings of a plan for the US to launch an invasion of Latin America in 1798, at the behest of Venezuelan revolutionary Sebastian Francisco de Miranda in some conversations with Rufus King, the US ambassador in London. The US would provide an invasion force of 50,000.
Except the U.S. didn't have 50,000 troops and the militias would refuse to serve in such a venture.