Sudden power vacuums are often filled by the most opportunistic individuals in human culture. People who are frequently more concerned with personal gain over the collective well-being of the group. It's why assassinating heads of state usually just makes the situation worse.
Plenty of people stepped into power vacuums not to make themselves rich but to save their nation Napolean, Tito, Cincinnatus, arguably George Washington.
Just like in human analyses of geopolitical situations, the explanations that rely on broad abstractions of human nature or resource competition and paint a teleological narrative always end up breaking down when you do a deep dive into the history and specific circumstances. When you get into the nitty gritty of every unique geopolitical situation it's actually much more difficult to pull out a generalizable lesson imo. At some point we have to accept that we can't cross the same river twice
I think some of the individuals who died were key in linking the two groups (they were "the glue" that prevented disruptive aggression), and after they were gone, the split cemented and later turned into aggression.