From 1910-1945, each country's richest 1% lost a lot of their wealth, all falling to (somewhat) similar levels. But in the time since, different countries 1% have built up wealth at very different speeds.

This suggests that a country's policy can actually have some effect - a lot is beyond each country's control, but it's not hopeless.

This is based on reading Thomas Piketty's "Capital in the Twenty First Century" (I'm halfway through) - really good read if you are interested in this.

I would wager that the two World Wars impact on capital had a lot to do with the decrease of the 1%'s wealth.

Not to mention absolute destruction of capital. Not just casualties of war, but capital investments that are either lost or used up in the process of war (airplanes, boats, fuel, etc)

This is basically what I was referring to, along with the redistribution and redirection of capital towards the "war effort."

Property, like matter, has an attractive quality similar to gravity: large clumps of property attract other property more than small clumps of property do. Given enough time and stability, the end state is usually one entity having (nearly) all the property (a star), or a few entities existing in (long-term) balance (like binary, trinary, quaternary, ... star systems).

But stability doesn't really exist in the Universe - there's always a low degree of redistribution going on between the clumps (trade). And clumps can explode into smaller clumps (people die, and the property is inherited/distributed -- Immortal entities like corporations sort of escape this thing).

Wars (and revolutions) are indeed the major disruptor, as it evens out the playing field (mostly by removing a lot of the property so everybody's equally poor). It's in the interest of the big clumps to keep the little clumps from getting too desperate, or from getting any funny ideas about redistribution of property, or from possessing the ability/organization to act on those ideas.

In the absence of sudden and violent (thus unpredictable) disruptions, the big clumps can accumulate and plan sufficiently to slowly work their way into an optimum state: balancing their continuous growth (faster than the smaller clumps) with the suppression of those to stop them, without tipping the balance into revolution.

The longer a system of clumps stays stable, the less likely it's going to become unstable. Until you get an outside disruption (invasion, natural disaster, plague, etc.) which is usually how long-lived and stable societies ultimately perish.