France sold the northwest as part of the Louisiana Purchase, Mexico sold Texas to California, and Russia had prior ownership to Alaska.
France
They purchased it from France.
ALASKA.
The US acquired the territory of Florida from Spain ceding it to the US.
In 1846 Britain agreed for the US to take control of the territory
In 1898 by Act of Congress.
Florida
Hawaii is the westernmost US State but Guam is the westernmost US Territory.
Yukon Territory
In 1898 as a Territory by Act of Congress.
American Samoa.
Yukon Territory