People want to move west to gain land, for access, religious reasons, and some people were forced to go west.
Lewis and Clark
President Jefferson purchased Louisiana from France in 1803 and it doubles the territorial size of the U.S. Jefferson then decides to send Meriwhether Lewis and WM Clark to explore the Louisiana territory. Lewis and Clark kept a record of all their discoveries and eventually was accompanied by Sacajawea, she was such a huge part of the expedition due to her being an Indian. Being a Indian, Sacajawea spoke the language and made Lewis and Clark less suspicious about being in the Indians land.
Indian Removal Act/Trail of Tears
The Indian removal act moved Indians to reservations west of the Mississippi river. Even though the supreme court ruled that Cherokees can keep their lands President Jackson goes ahead with the Indian Removal Act anyway. The Indian Removal Act lead to The Trail of Tears which is when Cherokee and Eastern tribes are forced to move to Indian territory. Many Native Americans died from disease and starvation on their more than 2,000 mile walk.
Mormons started migrating to Utah for religious freedom, they were led by Bringham Young. The Utah war was a armed confrontation between the Utah settlers and the U.S government allows Mormons to stay in Utah.
http://www.u-s-history.com/pages/h337.html - This website talks about manifest destiny and also has links to people involved in expansion and other effects that happened because of expansion westward.
http://www.nationalgeographic.com/lewisandclark/journey_intro.html - This link sends you to a interactive journey through Lewis and Clark's Expedition.