Here's why:

* Collision: The Appalachian Mountains formed over millions of years due to the collision of the ancient supercontinent Pangaea. This collision involved the Eurasian and African plates (which were once joined) with the North American plate.

* Folding and Uplift: The immense pressure from the collision caused the Earth's crust to buckle, fold, and uplift, creating the Appalachian mountain range.

It's important to note that the collision occurred hundreds of millions of years ago, and the Appalachian Mountains are now considered an "old" mountain range, significantly eroded and much less dramatic than the young Himalayas, for example.