- May 2014
Bargaining chips for peace negotiations. No need to dwell on that as it was a colossal flop.
Florida was IMO a strategic acquisition. Otherwise a foreign state(s) would control all means of ingress and egress to the Caribbean basin. Florida was a pestilential swamp until the very first couple of decades of the 20th century.
Other than Alaska the other expansion was for lines of commercial trade. Asia was a commercial magnet as soon as the US gained the West Coast. By the age of steam, and the establishment of a modern US navy, coaling stations were a strategic necessity. As to the US Virgin Islands - I got nuthin' .