Westward expansion dramatically shaped the face of our nation in many ways. Obviously the size of our nation grew tremendously beginning with the Treaty of Paris (1783) that defined our nation as everything east of the Mississippi River. The Louisiana Purchase (1803) doubled the size of our country, and the Texas Annexation/ Mexican Cession practically doubled it again.
As a result of this dramatic increase in land immigrants and slaves by the millions came to America to work the land, both voluntarily and involuntarily. As new people came to America, a plan had to be put into place for the orderly expansion of or nation. The Northwest Ordinance servied that purpose well, and new states began to form.
The addition of new states exacerbated the problem of slavery in the United States, as the uneasy balance of power of our nation was threated by the addition of new states and whether or not the would be a slave state. In many ways, westward expansion could be considered a key cause of the Civil War, though it is often overlooked.
Regarding industry, new industries popped up to service these new lands with the greatest being transportation. Trains and steam engines helped facilitate travel and spearheaded new industries to build the necessary machines and employed thousands in the construction of infrastructure... a budding new industry in of itself. Obviously the discovery of gold in California in the 1840s drew millions of people to the west coast in search of riches, and service industries blossomed to service those people. Additionally, when the lure of fast money didn't pan out, those people sought out work or land ownership instead.