> What makes land and people on one side of an arbitrary line so different from land and people on the other side of it?

Cultures? People on one both sides of the border generally have different culture and hierarchies of values. Thanks to borders, every nation gets to organize their piece of earth as they see fit (at least in democracies).

I don't think that applies anymore these days. I am from Poland and culturally I have more in common with most Germans than with many of my compatriots.

And my point is that the idea of "their piece of earth" is outdated. Apart from silliness and unnecessary politicians it leads to real problems, like countries deciding that they will burn oil and coal on "their piece of earth" and not care about climate catastrophe at all.

I am Polish too and I’d say were are on average very different from the Germans. A common, Polish-German state would be very hard to govern to due constant conflicts in values.

A lot of Germans feel the same about the Bavarian-German state.

Then what about Switzerland who speak 3 langues (4 officially). We talk English together and the French part is generally more focus on France than Switzerland (I'm from that part)

I guess you are still very distinct from say Belarusians or Japanese? In a world with no borders, the Swiss, Belarusians and Japanese would need to somehow agree on a common set of values that would govern this borderless world. And it’s hard enough to agree on policies in a single country.

We already have a lot of nearly-worldwide treaties, so there is something like a common baseline already.

I'd say it's enough to look at the US as an anti-example of how politics look like when you create a giant political body which governs people of radically different value systems. IMO, the solution is to pass more power down, to local bodies, not up, to continental or global behemoths.

The problem is that more and more issues are global. No single country can fix the effects of climate change on their territory, you need to cooperate on a global scale to do that.

Same e.g. for combatting tax evasion. Many other areas do not strictly require transnational collaboration, but it's immensely helpful. For example, the power network in Europe is incredibly resilient because it is shared across dozens of countries. So every individual failure is rather small, even if it takes a large nuclear power plant offline.

There's some funny business going on in the phrase "their piece of land". It's not like each citizen has the same ownership rights of every bit of the country. If I own a bit of land in Japan, why does it suddenly become "their land" for the purpose of determining laws?

It has hardly ever been that clean cut in practice. And the attempts to enforce the strict divisions have not been pretty.

If you want to have government provided services funded by taxes, you need to determine who will be paying those taxes. Borders provide a clean division between the paying customers for a particular government's services, and those who are not.

This strikes me as a naive, European way to understand borders (governments are services, you get to choose who to pay your taxes to). Most of the world's people are born to governments they do not endorse, and do not want to pay taxes to, yet they still have to. I was born in a shitty country and even though I've been living in the US last 5 years, I still have duties to my home country such as taxes, military, community service etc... And since I'm not a US citizen yet -- even though everyone I care and my life is here -- I cannot reject these duties to my country since I need its services such as providing me with a passport, an embassy (for legal help) etc. Besides US can randomly throw me away any time it feels like, and the one country I can always go is my home country.

I love how these sort of bureaucratic things are so simple in the EU. For the rest of us, it is much more complex, and for most of us living in a country we like is a dream that can hardly be achieved. Nearly all my childhood friends living back home are trying to escape their country but it's not that easy (you need to find a job that accepts H1B for US, or equivalent bureaucratic mambo jambo for the EU).

But you did decide that you didn't like how your original government runs things, and you switched to a different government. That's very much in line with the European understanding of government. Your only problem is that the US is extremely picky with accepting new customers.

Also note how many of your problems are exceptional. Few countries raise taxes from money that never enters or leaves their country, and military service requirements are often paused while you are abroad. You have it harder than most.

USA is an example of raising taxes from money that never enters or leaves the country, I think. US citizens pay taxes from income abroad when they live abroad and non-residents pay taxes for money earned from US companies (like I do).

Agreed — but do we really need so many governments? Why not have a local regional level (city/region, where you live and where things really matter to you) and then a continental level (EU, US, China, Russia, etc)?

I really do believe that we have way too many governments, and borders are an artificial construct used to support politicians.

Speaking in vast generalities, a continental level government seems to get big projects done better, but also seems to often treat their citizens much worse.

Personally I like that the world has both types of governments. It provides, to some extent anyways, redundancy against the failures of each type of government.

There is a need for rule setting. Starting from rules about capital crimes to local organisational of roads or house construction. If we rule out anarchy as a way to rule this this needs some form of governing body and the exact form of those have cultural, geographic, population, ... differences which need to be respected. There is no global agreement on many of those things. How are different crimes valuated and punished, is a high density road network needed or more public infrastructure. Doing those things in smaller units has benefits, for doing that you need borders to define which rules are valid where. Of course such borders are to a large degree virtual (i.e. you often don't see the exact city borders) and not borders with guards and fences.

On top of that then come all sorts of historic, cultural, ... reasons to "protect" each other which have all complex reasoning. Power-hungry politicians are only a quite limited reasoning, as many borders are supported by societies (by far not all, though)

It goes back millions of years with territorial animals but hopefully we are gradually getting over it with the odd glitch like Brexit en route.