Life in the cities at the time was becoming over crowded as newcomers arrived in the country on a daily basis which caused slums to start developing. The eastern cities were mainly shipping centers and manufacturing was not that important. The industries that did exist were ship building and some barrel making of some type, which of course were tied into trade and commerce. Garbage littered many city streets and even goats and hogs, chickens and sheep were permitted to roam free. Since many of the streets were still undeveloped (not paved yet) it made for a very haphazard way to travel. The lack of sanitation so often led to epidemics of contagious diseases, which the most dangerous of was "cholera". The cause of this disease was bacteria in polluted water which was un- heard of at the time.
All this added to a national desire to expand their territories west which created the slogan "Manifest Destiny" which meant that the people of the country felt that there boundaries should be all the way to the pacific.
Expansion would alleviate most of the overcrowding in the cities and lead to more jobs and better prices for products and trading and buying.
With the advancement of the steam engine rail road and steamboats became the new mode of transportation which provided a faster more efficient way to move people and goods west and east. Since wagon trains are now moving large amounts of people and goods west what happens when encounters with the western plains Indians are not ready to except all of these new people who now occupy the lands they were always able to move from one place to another on and are not willing to allow them to plant there new lives? There was lots of fighting killing...