Extremism
Extremism only gets you more extremism.
In the early stages of creating a Jewish homeland in Palestine, most of the Jews and Arabs were happy to coexist together. A very small minority of Jews weren't - they wanted Arabs out and the promised land to be for Jews only. A very small minority of Arabs weren't - they viewed the Jews as invaders in their territory and wanted them to get the hell away.
Since the vast majority didn't agree with either minority, the two fringe groups turned to violent tactics. Jewish groups arrived in the middle of the night and bulldozed villages, sometimes with people still in the houses. They went through other villages and killed everyone - men, women and children. Their intention was to scare the Arabs into leaving the country.
Arab groups started bombing Jewish buildings and infrastructure, eventually using suicide bombing as a tactic. Their intention was to scare the Jews into leaving the country.
Unfortunately, the effect is to horrify and terrify the moderate people on both sides. Their grief and anger overwhelms their empathy for the people on the 'other side'. The extremists aren't really affected - their views are just confirmed. But people who were previously happy to share the country now just want someone to pay for what happened to their mother, granson, daughter, cousin, nephew, friend.
And so a much larger slice of the people are now willing to take extreme positions, and use extreme measures. The longer it goes on, the more polarised the two sides become.
I don't know what happens after that. Maybe it just escalates until one side wipes the other out. I'd like to think that isn't the only outcome.
Perhaps enough people on both sides eventually realise that the battle is futile and only results in more harm and hurt to everyone. Perhaps getting revenge for past wrongs becomes less important compared to preventing even worse wrongs in the future.
Maybe the people retreat from their poles of extremism and realise that it is the extremists on their side as well as the other bear responsibility.
Of course, sitting here in nice safe little New Zealand with no actual experience of this sort of thing, it's quite likely that I'm just talking outta my ass.