The push westward during the early 1800s was fueled by very high birthrates. The 1800 census recorded a population of over 5 million. By 1810 it had jumped to over 7 million— a 36 percent increase. By 1820 the population was approaching 10 million, almost doubling in twenty years. A great flood of emigrants from Europe further increased the country's population explosion. In Europe, food shortages, wars, and oppressive taxes combined with their own population explosion to produce a huge outflow of people to the United States. In 1821 the Irish potato crop failed—the first of many such failures, with the worst occurring during the 1840s. By the end of the 1840s, almost one-third of the Irish population had come to America. The British organized a sealift to Canada and America at almost no charge to the desperate Irish farmers. As these Irish emigrants poured into America's harbors...