...The Irish were driven from their country due to the great Potato Famine of 1845. The potatoes, Ireland's main source of food and money, turned black with disease, and for the ensuing five years a famine ravaged the nation. One million died, and another 1.5 million emigrated to the U.S. Many Germans left their homeland due to similar situations in the States: the industrialization of economy put hundreds of farmers and artisans out of the job, forcing them to look for work in America. The Germans developed a unique form that allowed for the conservation of their culture. Immigrants formed predominantly German communities by clustering. The influx of immigrants added to the already large population of poor workers. These workers formed impoverished urban communities called slums. The new wave of immigration made America the cultural melting pot that it is today. As the economy began to settle in the North and South, settlers began to look westward. Most of the territory east of the Mississippi had been made into states, and many Americans were eager to expand into the immense territory of the Louisiana Purchase. Before 1776, they had been slow to settle the land, which was called the back country. After 1800, however, the back country became the frontier, which was defined to be sparsely populated or unexplored lands. As the eager settlers drove westward, they created small agricultural communities. These small communities soon developed into towns, and towns into cities. During this period, Americans looked ever westward. They gradually explored the frontier, expanding from the Mississippi all the way to the Pacific. During this time of westward expansion, settlers traveled by wagon nomadically looking for arable farmland on the frontier. Once they found a suitable spot, they "squatted" down on the land and unofficially claimed it as their own. ..