Because the US lost the War of 1812
You mean before the Mexican-American War? That was the Nueces Strip.
Napoleon sold the Louisiana Territory to the US to finance his European War.
Yes, Guam became a US Territory as a result of the Spanish American War.
It became a US Territory.
No. We lost territory.
The American public today would probably approve of the US acquisition of Guam and Puerto Rico, but not the Philippines.
ANSWER
Texas Territory
True, Guam became a US Territory as a result of the Spanish American War.
The Louisiana Territory which was purchased by the US in 1803.
After the Spanish-American war,Cuba was granted independence and Puerto Rico became a US Territory.