When Lewis and Clark left for the great expedition in May 1804, most of America was still being developed and this was one of the main goals of the Lewis & Clark expedition, to discover the American regions that were yet to be discovered. In addition to that, the explorers who followed Missouri through the modern day Kansas City, Missouri and Omaha, Nebraska then crossed the Rocky Mountains and descended by rivers until they reached the Pacific Ocean. Other than the rapid change of the weather conditions, difficulty in find the appropriate route to use was also a barrier to their quest, in some scenarios, they had to change routes a couple of times before finding the perfect passage. It is also noted that there was a time when they got lost and had to retrace their steps before finding the correct path. The overall achievement of the expedition which came to close in September 1806 can be categorized into social, political and economical form. The biological significance of the expedition cannot be left out either. From a biological point of view, they were able to name hundreds of species of plants and animals, they also carried samples of the plants and animals back to American research laboratories for further study to establish the origin and other biological facts of the species. America opened its doors for business with the nations in the west, this also was boosted the positive ties that the nation established with the American Indians. The United States of America was in a better spot to claim the Oregon territory which no one had done.