In that case, why do we have ~200 nations instead of a single world government? Clearly, sovereignty matters to groups of people.
"Sovereignty of money does not matter to LARGE groups of people" - might be a more defensible argument.
Italy alone used to be a dozen+ independent city states. Divided the world 200 ways seems like a lot unless you look at how much it's been divided historically. And in comparison, that's extremely centralized.
Stealth, space supremacy, global surveillance, carrier groups, strike wings, nuclear arsenals, reaper drones and all the other crazy battlefield robot tech in service or development can cut to pieces any obsolete nation state military, let alone some rebels armed with cheap 3d-printed guns.
So why isn't the US (which has all this tech) winning in Afghanistan over some rebels with AK 47s? Likewise Vietnam after literally a decade of fighting.
Weapons superiority is one factor in winning wars. Likewise, to address the gp's point, the history of political organization is partly driven by military technology.
And the current struggles of the American military only result in hundreds or maybe thousands of American deaths, which historically, would be a mere rounding error. Afghanistan, Iraq, Syria, et. al. are a mess, but they don't come to a significant human cost to America.
The United States and its voting populace doesn't really care about whether or not developing countries are wartorn, and quality of life is decimated—America and other states have completely destroyed the backbone of several societies in the Middle East and caused the deaths and relocation of hundreds of thousands of innocents, but you don't feel the pain of that when you live states-side. So the country has little incentive to quickly resolve these conflicts besides the bad PR; ongoing conflicts mostly buy time for protracted, proxy diplomacy with other major powers to lay claim to natural resources, and aren't viewed as conflict with a tangible human cost.
What's interesting is to consider that while the world is very centralized in the sense you described, "day-to-day" operations are even more decentralized than ever. That is, (very generally speaking) order is established and maintained, and people go about their lives without huge, burdensome micro-management from "above" in the important aspects of their daily life.
It probably turns out that the most consequential decision-making affecting the modern person's daily life is happening very locally in the social & spatial/temporal sense. So, in that way, authority is effectively decentralized.
The number of states waxes and wanes throughout history, there's not a clear trend.
The long run trend is very obviously toward a single government. Consider that until the Sumerians established cities less than 7000 years ago, humanity was just thousands small traveling groups of nomads with no defined borders.
Sovereignty gets a lot of lip service, but in practice most people don't really want it. It's a lot of work.
Is it? I believe there are far more countries now than 30 years ago.
We seem to have some more powerful international organisations now than a century ago, but earlier than that we had world spanning empires, and Europe was less than 10 countries before WW1.
I want to believe that we're heading towards a star trek like unified post scarcity planet, but I'm unsure we're not just seeing a local trend.
Much how King Arthur, Lord of the Britains was not known to the members of the anarcho-syndicalist commune.
Hmm, I think you will have to justify that statement, rather than simply claim it is a very obvious fact. Generally, there were fewer governments in the past as compared to the modern day.
If the answer is no then your point stands. However I tend to think that the answer is in fact yes and the trend does indeed seem to be toward centralized world government given a long enough time period.
all we need is an event that demonstrates the need for a world government - for eg a massive asteroid headed at earth or a planetary scale food drought to see these systems implemented.
the world is stagnating
It's easier for powerful central organizations to influence smaller countries which are divided against each other, while believing that they are relatively independent.
Also: latency of information transfer and the speed of light, which lead to local variance and central filtering of changes which are allowed to diffuse elsewhere.
It's more likely that the cities will become the dominant form of a citizen's home sovereignty rather than a nation, with only a few national boundaries around the world. People are inherently tribal and human behavior isn't changing anytime soon but countries are quickly becoming stretched too thin to keep up with all the varied and changing populations and their needs.
Coase won a Nobel Prize for this. Simply, the trade-off between bureaucratic inefficiency and economies of scale.
The correct starting question is "why do we have 200 nations, instead of millions of individuals and families living autonomously?" and the answer is: human beings are basically tribal people, and military conquest.
And then the answer to your question about why 200 is that military conquest never got any farther before the atom bomb eliminated direct warfare between major nations.
My point is that sovereignty, innovation etc. are valuables which centralization can't deliver. "Monopolies will maximize profits and therefore, under-supply the product" is Economics 101. So, yes, economics of scale and network effects do encourage centralization but there are counter-balancing forces.
What we need is protocols that allow a sliding scale as opposed to non-interoperable silos. DNS, TCP/IP, Git delivered exactly that. While GitHub has the scale and network effects, plenty of people are happily using GitLab, BitBucket etc.
Deltas in space and time plus the fact face to face conversations give you a better idea of the sender's mental state. Comms over the Internet are untrustworthy, if you don't have prior experience with the sender.
Also, language, which is related to deltas in time and space.