Montana is a big piece of land in northwestern United States that has changed its shape and size over time as different people and events happened. The territorial evolution of Montana means the different ways that Montana's boundaries, or the lines that divide it from other places, have changed through history.
Long time ago, Montana, like the rest of the United States, was inhabited by Native American tribes. These tribes lived in different areas and had their own territories. But later on, Europeans came to America and began to claim the land for themselves. The first Europeans to arrive in present-day Montana were the French, who established trading posts in the western part of the state in the 1700s.
In 1803, the United States bought a huge piece of land from France, known as the Louisiana Purchase, which included the land of what is now Montana. At first, Montana was part of the Missouri Territory, but as more settlers moved in, Montana became its own territory in May 1864.
Montana was originally much bigger than it is now. It included parts of the states we know today as Wyoming, South Dakota, North Dakota, and even parts of Idaho and Nebraska. But as these states became more populated, they were split off from Montana and given their own statehood.
Finally, Montana officially became a state on November 8, 1889, when it was granted statehood by the federal government. Since then, Montana has remained the same size and shape, making it the 4th largest state in the United States.