While I am known to show atheist tendencies, I have to say that religion has no lock on inflaming Man's inhumane traits. Politics and greed are also contributors. Also, total stubbornness is a big factor. I'll bet some folks are ready to ask me if I'm feeling well by not bashing religion - but I believe that in this case, religion is not a primary cause. This is one of those older factors that, in Germany in the early 20th century, was called Lebensraum - literally, room or space to live and (implied) to grow.
Despite it being a wise piece of advice, "live and let live" doesn't usually work very well because it seems to only take a short while for the "anger pot" to bubble over. Folks (like Hamas) can only live and let live for a while before they want more without regard for who would lose if they win. For them, it is the inability to see others as equally deserving people. Religion often tries with basic principles that should - but apparently do not - stick well with their congregations. "Do unto others as you would have them do unto you." Hamas launched deadly rocket attacks, so Israel did unto them what they had done to Israel. Well, DUH! What did they expect?
Sadly, we have an inbred trait we got through evolution... call it "territoriality" or "tribalism" or pick another name. Our saurian ancestors needed a certain amount of territory to provide adequate food, so the thunder lizards defended that territory against intruders. Now we protect our territory (or try to) against all who are different. It would represent a big diversion for this thread but I believe a case could be made that at base, Americans object to illegal immigrants as an offshoot of this some inherited evolutionary factor - the protection of me and mine against thee and thine, which is another form of tribalism.
Putting the nice parts of religion aside, we have two tribes trying to kill each other off for possession of land, Sadly, one has such a deep belief that their god has promised them the land, that they will stop at nothing to acheive that goal in the name of their deity.
The Jews have a financial, and political hold, in the US, so the pressure is on the US to back Israel. The UK who should have brokered a two-state solution but were too weak to stand up to the US/Israeli demands and the US finally recognised the state of Israel with new boundaries. That was the reboot for the Israelis to restart their take-over of land, outside of their borders and it has remained that way since 1948.
Now, the Israelis have a monster at the helm who won't be happy until all the Palestinians are either dead or have fled to neighbouring countries, which would open up a new can of worms.
The inbred trait, you mentioned, was a natural part of the growth of civilisations. In the UK, settlers crossed the land-bridge from Europe around 10,000 and began settling down. The build homes, they build enclosures for their animals and, naturally, defended their space. It was, and still is, a necessary development in a peoples'
There is no doubt that once you create a deity that you can get permission from to do whatever you want, the trouble starts. All civilisations have done this, to a greater or lesser extent, during history; this is just the current one.
The world sits by and watches the main players, and profit from it.