Why did immigrants come to the unites states during the second half of the nineteenth century?

Immigrants came mainly because of the picture of the United States compared to the rest of the world. Imagine if this country who just started out a century and a half ago suddenly started making millions, with many entrepreneurs making bank. Also, many countries that said immigrants came from were poor. While many immigrants came, almost all ended up living normal or sub-par lives. This is part of the Gilded Age.