Mexico, Spanish Florida, Louisiana and Oregon Country.
Step-by-step explanation:
The expansion of American country is an important event in history. After Independence, all the colonial states were joined together forming a country called the United States.
This expansion process was started in the 19th century effectively. In 1803, Louisiana state was purchased which was the French Territory. It was bought for 15(approx.) million dollars and that doubled the American territory's size. Spanish Florida was acquired by the year 1821.
Oregon Country which was situated near the pacific ocean also acquired which was shared with the British for some time. In 1845, the outcome of the Mexican American war directly gained the north part of Mexico and that was included along with California.