It's easy to forget that not everyone has been keeping up with the Israel story, but the pro-Israel propagandists have been out of late, serving as a reminder, so here's my outline...
Israel was founded in 1948 by edict of the UN. The rationale was that Jews had been beaten up a lot and needed a nation of their own.
The Palestinians are the people who were living there at the time. They call this event the Nakba ("catastrophe").
(And now you know more than most people who watch television news.)
In 1967, Israel conquered adjacent territory (the "six days war"), and since then they've been a rouge state by UN standards.
(And now you know more than everyone who watches television news.)
The American left does not call for the destruction of Israel, but rather for it to return to it's pre-1967 borders. Israel says those borders were "non-defensible". They also have moved in "settlers" as fast as they could to complicate any negotiations.
There's a monotonous pattern toward events in the Middle East. Negotiations collapse in out-breaks of violence, with lots of finger pointing. Sorting out whose fault this is seems complicated, though left-wing observers such as Chomsky typically blame Israel.
You will then hear complaints about Israel's actions being a "disproportionate response", which is to say that they've killed a lot of innocent civilians again.
Israel gets a lot of money from the US to do all this: we fund around a third of it's military.
It would seem that nothing would be simpler than for the US to get Israel to tone-down it's act, but instead any successful American politician is required to recite a pro-Israel line.
That includes Hillary Clinton: as Senator of New York, she invited it's citizens to consider how they were feel if they were being attacked by Canada. (I would ask how they would feel if the UN wanted to put Israel in the Brooklyn.)