Why can't something as complex as a historical change have multiple causes? And when the rise of social/economic inequality is such a clearly-evidenced part of

Why can't something as complex as a historical change have multiple causes? And when the rise of social/economic inequality is such a clearly-evidenced part of the mix, why should those who have reaped unsustainable benefits from an unfair system not share part of the responsibility? I'm not exculpating the ethno-nationalist forces (leaders or followers). They are dangerous and wrong (and their more moderate fellow travellers have allowed, for ignoble motives, nasty stuff to fester now for decades). But when you have a rising class allocating ever rising shares of the world's wealth to itself, resentments will build. The Gates & Thiels of this world are fairly invulnerable and can buy themselves more fiercely guarded and gilded palaces to hide in (ever higher as the oceans rise). But for the rest, you would think even self-interest (let alone ethics) would have encouraged them to use their wealth and power to argue for a fairer polity. They didn't, and it's too late now: here comes the backlash with dizzying speed. It looks to me like we're beyond reason and are headed for widening violence and wars. I hope I'm wrong.