'From the river to the sea:' What to know about the pro-Palestine slogan that's roiling American politics right now

"From the river to the sea, Palestine will be free."

At pro-Palestine protests and in activist spaces, it's a rather common refrain, referring to the entirety of the land from the Jordan River and the Mediterranean Sea — land that includes Israel, the occupied West Bank, and Gaza. 

But some Israelis and Jewish people argue that the phrase has a far more sinister meaning — and Rep. Rashida Tlaib's defense of the term is generating significant controversy for the Michigan Democrat within her own party.

Here's what you should know about the current controversy over the slogan — as well as its origins and contemporary use.