-The increase of immigrants
-The aftermaths of WWI
I really don't know if what I said is correct, but I just thought of it as of what happened before 1920
Answer:
she is praising the U.S for taking in the world's immigrants and seems to be saying the U.S will benefit from it.
This expression is by far mostly likely ascociated with President Lincoln during the Civil War. He famously did not want to punish the southern states in order to headl quickly.