Territorial evolution of the United States
The United States is a big country made up of lots of smaller pieces. Over time, these pieces changed and the borders between them moved. This is called territorial evolution. For example, the United States bought the Louisiana Territory from France in 1803, and this made the country much bigger! Or, after the US won a war with Mexico in 1848, it got a lot of new land in the Southwest. Over time, our country has changed a lot and this is called territorial evolution.
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