Wave of revolutions in Europe. Collectively known as the Revolution of 1848. This led to mass emigration of these refugees into industrial cities of the United States as well as to other locations around the world.
Seneca Falls Convention (first convention for women's rights) 1848.
Economics
In the mid 1840s several harvests failed across Europe, which caused famines. Especially the Great Irish Famine (1845-1849) was severe and caused a quarter of Ireland's population to die or emigrate to the United States and Canada.