(Thanks to Pamela Weintraub for the tip.) Although it may seem hard to believe sometimes, not everyone has spent years closely following the past history and current intricacies of the Israeli-Palestinian conflict and the larger Arab-Israeli conflict in which it's embedded. People who haven't may be interested in a basic primer on the historical background to the latest Israel-Gaza war put together by by Zack Beauchamp at Vox:
11 crucial facts to understand the Israel-Gaza crisis
I think this is pretty clear, accurate, unbiased, and useful. A few small caveats and other comments:
=> Item #1 is headed: "The Gaza Strip used to be part of Egypt, and is totally separate from the West Bank". Yes and no. Gaza was never technically "part" of Egypt. From 1948-1967 it was controlled by Egypt, while the West Bank & east Jerusalem were controlled by Jordan. (Jordan did formally annex the West Bank, but almost no other government recognized that annexation as legitimate.)
=> Gaza is often described as the most densely populated place in the world, but that's simply wrong. The heading of item #2 might seem to be offering a slightly more qualified version of that common refrain, since it says that "Gaza City is among the most densely populated places in the world". But as Beauchamp's own discussion makes clear, things are more complicated than that heading might seem to suggest. For one thing, "Gaza City" doesn't = Gaza. It's one of several cities in Gaza, the biggest one. The urban areas of Gaza are certainly quite densely populated, even though they're not the most densely populated—according to one estimate cited by Beauchamp, Gaza City is "the 40th most densely populated urban area in the world"—and those urban areas are where most of the fighting and bombing happen, because that's where Hamas and other jihadist groups are dug in. Overall, Gaza is less densely populated than plenty of cities and metropolitan areas of comparable or greater size around the world, including (for example) Singapore and Tel Aviv/Jaffa.
=> As Beauchamp correctly notes in item #6, in 2006 there were elections for the Palestinian legislature (representing both the West Bank and Gaza), and—to most people's surprise—Hamas won a small but solid majority of the seats. It may be worth mentioning that they got a plurality (about 45%) of the overall votes cast,, not a majority. Nevertheless, the fact is that Hamas won fair and square according to the election rules, and their victory was both stunning and consequential. They got more votes than Fatah, the ruling party headed by Mahmoud Abbas, while the other 12-15% of the votes were split between various smaller parties and lists. About a year later, there was a violent showdown between Fatah and Hamas in Gaza, in which Hamas beat Fatah decisively and seized complete control of Gaza. Fatah has kept control of the West Bank, and Mahmud Abbas remains the formal (and internationally recognized) President and head of the Palestinian Authority. (There have been no more elections since 2006.)
=> Item #11 makes a point which is worth emphasizing and elaborating a bit further. Egypt is now ruled by a government strongly hostile to Hamas (and favorable to Mahmoud Abbas and the Palestinian Authority). One factor that complicates the present situation is that important elements of Hamas's agenda involve, in effect, getting concessions from Egypt, not from Israel—especially in terms of easing restrictions on movement across the border between Egypt and Gaza.
Actually, item #7 (about Israel's blockade of Gaza since 2007) and item #11 (about the Egyptian role in this conflict) are closely connected. Egypt has participated in this blockade, to varying degrees—in fact, without Egypt's participation the blockade couldn't really be maintained—and recently Egypt strongly tightened up its part of the blockade.
—Jeff Weintraub