What was one reason that native-born americans felt more threatened by the "new" immigrants than they had by the "old" immigrants?

One reason that native-born americans felt more threatened by the "new" immigrants than they had by the "old" immigrants was that the "new" immigrants brought different cultures and languages. These Nativists believed they were the true “Native” Americans, despite being descended from immigrants.

1) one variable is tested2) a control is used