Why did Jurgis and Ona decide to go to America in The Jungle?

In a nutshell, they immigrate to have a better life.  While in Lithuania, they experienced some major financial difficulties.  A friend of the family tells them about all the opportunites in America so they decide to go.  In Lithuania, Jurgis and Ona did not have enough money to marry, but they thought they would be able to have all they wanted, including money to marry, when they moved to America.