Which of the following drew millions of immigrants to the united states after the civil war?

These immigrants usually referred to as settlers, opted in the main for farming, ... through the 1880s, about 15 million immigrants made their way to the United States, ... Particularly in the decades just before the U.S. Civil War (1861-1865), this ... the decades after the Civil War, as the sources of immigration shifted so too did

B." to guard against " is correct answer