The history of the United States is a history of people on the move. The Native Americans came to North America thousands of years ago. Some of them built villages and stayed there, but many moved from place to place. The first travelers from Europe came to live in an unknown land. At first, they stayed near the coast, but then a few brave men went west, far into the country. Two of them were Meriwether Lewis and William Clark. In 1804, they started on their long journey from St. Lois, Missouri, to the Pacific Ocean. They followed the Missouri River west, went across the Rocky Mountains, and f