The initial increase in immigration during the 1830s and 1840s was caused by improvements in shipping, more rapid population growth in Europe, and the potato famine in the latter part of the 1840s, which affected not only Ireland but also much of northwest Europe.
The early 1800s saw the United States quickly grow in size. New immigrants and new land meant a bigger and stronger country. It also meant displacing thousands of Native Americans and the continued spread of slavery.