I think you make some good points but imo you still can have a stable world order in a "Unipolar World" with good leadership governing, something we are currently lacking.
As to the Proxy wars during the Cold war, the US won most of them with the exception of a few.
Yeah, I don't know, it gets very complex.
To sort of "dumb it down," odd numbers in most social/global systems are more difficult than even numbers. For example, having 2 children is usually better than 1 or 3. The 1 kid may be strong, but he's alone. Having two 2 strong kids: they might fight with each other "in the house" but they are not going to kill each other. In a social setting they protect each other because of a common interest, and it's less likely that any one will challenge two strong brothers and thus, the friends (allies) each of them have. Having 3 Strong kids (3's a crowed): It will always be 2 vs. 1... and so on.
Same with commerce. On strong company will start to face competition from several places. 2 dominant companies makes others think a lot longer about getting into a big stakes game. Home Depot and Lowes. Boeing and Airbus. The 3 american auto companies killed each other and have been dominated by Toyota and Honda from Japan and BMW and now Benz from Germany. Microsoft was the far and away leader for a while and Apple decided to get there stuff together and now there are two. Intel vs. AMD.
-These aren't exact analogies but they show the same concept.
We haven't had good leadership for the last 2 decades.
When the USSR fell, we i the west went into this "multiculturalism" and globalization trend, and nobody wanted to hear "nation building." Sadaam invaded Kuwait in 19991, something he would have never done a few years earlier (he got into the open boarder thing). Wars throughout Africa. Yougoslavia broke up into and is still having ramifications on the world today. Al-queda came about in the early 1990's, and UBL made his statement in 1995, "declaring war on america." The power base in the ME, is in chaos, and has shifted to Iran, who talks to the 1 "superpower" as though they're the 2nd superpower. Russia, isn't the USSR, but Putin acts like it is. NK, Iraq, many of the African nations and south american countries have either become failed states, or are close. Afghanistan is Afghanistan. General chaos as there is no more international order.
The power was held by the US and USSR, and when the USSR fell apart, it's power was up for grabs around the world. Instead of the west consolidating that power, we tried to all of a sudden create "great relations" with a superpower that just crumbled--instead of picking up the mess. With the oil prices that are already crazy, and China vs. India vs. Pakistan, all growing and consuming a ton of natural resources, it's not going to get better.
With one superpower, another on the verge (China), and India trying to quickly catch up, the "International System" is no longer a system, it's more like anarchy, where sometimes "enemies of enemies are friends."
The reason I mention the problem of doing the opposite of nation building, is because the "old rules" don't exist anymore. We are a country that's been perhaps the best with having so many cultures, but that's because of our short history. It's benefitted us to be a country of immigrants, as the Nation is young, but the combined history of the people who make up our country, which we draw lessons upon, is actually very long. However, as we're starting to see here, immigration throughout Europe (more recently) has caused many several countries to have mini-states within some state's.
The US had been pretty good with immigration because it was just assumed, those who come here will adapt to our society. Not divide and conquer, but people who came here would "Divide and Surrender" (i.e. immigrants would always keep their culture, but assimilation to the Nation was more important).
Now, we, as americans are being divided and perhaps conquered, from within.
Anyway, IMO, without balance, international stability is lost and the entire system is "reset" and we go back to the original state of nature, "survival of the fittest." Except, the population of the world has grown quite a bit, people want to protect themselves or take advantage of an opportunity, so more arms are sold--to everyone by everyone-- and more conflict becomes inevitable.
Anyway, those are just some of my thoughts. It's like a complex matrix now and I can't even touch the tip of the ice-berg.
Peace