The Lewis and Clark expedition impacted the United States of America profoundly. Thomas Jefferson and others who had led the effort to create a new nation in the former British colonies had long sought to expand the nation’s nascent borders. Very formidable obstacles stood in their way, namely the presence of the French and the fact that little was known about the land purchased from the French, let alone what lay beyond it. The first obstacle was effectively removed when Jefferson was elected president and successfully negotiated the Louisiana Purchase, which doubled the size of the United States and pushed its western-most boundaries hundreds of miles further out. The second obstacle was addressed through the commissioning of the expedition led by Captain Meriwether Lewis and the man he selected to accompany him as co-leader of the journey, William Clark. Together, and with considerable assistance from their Native American guide Sacagawea, and from Native tribes along the way, they succeeded in exploring much of the continent. They arrived at the Pacific Northwest in November 1805 two and a quarter years after their departure.
The impact of the Lewis and Clark expedition involved the considerable knowledge the explorers gained during the course of their journey regarding the geographic and topologic features of the terrain and of the peoples who populated it – in effect, the Native tribes who had proved so helpful in facilitating the group’s advance across the continent. With the knowledge accumulated during the expedition, President Jefferson was better able to make informed decisions regarding the westward expansion of the United States.
The Lewis and Clark expedition affected America in many ways. First of all, Lewis and Clark were able to map out not only the Louisiana Purchase, but the entire western United States. This helped people colonize the western United States. They were the leading pioneers to the western United States. After their expedition, many trails were made so that travellers could get to the west much more easily. Also, not only did Lewis and Clark map out the west, but they also discovered many new species of animals, plants, and birds. They also became friends with some indian tribes, who were able to guide them and give them more information about their land. The most famous guide was Sacajawea. Long after their expedition, people were still going to the west, and many of the western territories had already become states. The states were becoming more and more separated over slavery because more states would become slave or free. This soon led to the Civil War. Without Lewis and Clark's expedition, history would have been very different.