Why does most of the US population exist east of the Mississippi?

The United States evolved from thirteen colonies on the Atlantic coastline of North America. It then spread across the continent over the next couple of centuries. Since the United States' beginnings are on the East Coast (east of the Mississippi River), many immigrants have settled here. This region is also a very large industrial and agricultural area, which attracts many workers. Also, this is the closest part of the United States to Europe, where most of the US' immigrants have come from over history.