> But that's not necessarily stability

Yes, it is - it's an unjust stability, which is why I pointed out that the question of justice is separate from the question of stability. Do not confuse justice with stability. China and Russia are stable powers and Rome was a stable power, but none of them are democratically just.

> Do you think the Middle East would be more stable if Saudi Arabia were powerful enough to conquer Iran?

No, because that's a more complicated question than you think. Like I pointed out, large stable powers are threatened by asymmetric players. The US invaded Afghanistan and Iraq and defeated their incumbent governments extremely quickly, only to discover that American rule was unstable because of asymmetric threats in both countries. A theoretically (really, only theoretically) sufficiently powerful House of Saud could govern Iran, but there would be enough of a threat from asymmetric players to undermine the stability of Saudi rule in Iran. Being able to quantify the potential for asymmetric threat and accounting for it in a risk profile to try to present the case for or against invasion is, to my knowledge, an open research question in military science, conflict studies, game theory.

> If you want to avoid all violence, even at the outset, you have to constructively arrange for a balance of powers

Literally the explanation for why all of human history is so bloody is because for most of human history, the difference in military power between players was slim to none. Europe was a patchwork of warring fiefdoms with no clear central power (aside from Pax Romana) resulting in two world wars. Latin America was unstable for most of the twentieth century for the same reason (see above). Warlords continue to be a source of much instability across the African continent as much of the continent is run by governments which are too weak to effectively control the sum of their territories from the threats of warlords etc. I have absolutely no idea where you came up with this idea.

> structure of American government is renowned for having the foresight to vest powers in distinct branches in a manner designed to maintain a balance through tension

And the result is quite unstable. Each branch, internal to its own context, yes is quite stable - but the sum total is so unstable that 46 years after Roe v. Wade, there is still no consensus on abortion policy; 52 years after the adoption of the 25th Amendment, there is still no consensus on whether it permits the Cabinet to remove a sitting President who does not want to be removed; 151 years after the adoption of the 14th Amendment, there is still no consensus on the true meaning of "equal protection of the laws" across racial and class divides.

Rather, American governance is a case study in how projecting stability externally - both to the general American public, and to the world, each in its own context - can help to mask a deep internal instability, and how that internal instability paradoxically feeds the external projections of stability, for better (Pax Americana) or for worse (industry holding off on investment while it's unclear as to the extent of the trade war with China).