Wouldn’t removing or abolishing borders result in more invasions and wars, not fewer? Weak or unprepared nations would no longer have allied agreements for protection and would surely be under attack.

I agree, but those aren't the kinds of borders OP is talking about, I think. And it's a naïve simplification, in any case.

I interpret OPs point is about free travel and employment, without restriction or passports. The kind of "no borders" that exists in the EU: any citizen of a country in the EU can travel to, live in, and work in any other EU member country, without restriction, without limitations, and without passport.

It doesn't require, but is greatly facilitated by, a common currency; and as the EU has demonstrated, there's a lot of moving parts for this to function well. Having a common set of standards for human rights, having some basic economic model alignment, having mutual non-aggression agreements for a members... they're all essential components. Heck, I'd suggest that it'd be super-helpful if there was adopted a neutral, universal second language that all member countries require children to take a couple of years of in the public education system - a conlang like Esperanto (by virtue of sheer numbers of speakers), but certainly one where no single country has a advantage by having it be the natural native language, which excludes English.

Anyway, that's the kind of "no borders" I think OP is talking about, not the governance kind.

Why do you assume we need an entire government to do work?

It's because it's a one-party system masquerading as a two-party system.

liberals have a lot of "very serious people" who talk about the sanctity of the nation state.

Notice how there is no border between your town and the next one? Same, but on a larger scale.

You can just keep going where the border would be.

Simple. In the past there is no "border". You are someone from Frankfurt who came to Paris to set up business and there was no question asked.

A example that’s not borderlessness, but still interesting, was the Behind the Bastards episode on Harlan Crow which talked about how there was seasonal migration of people from Mexico into the US during peak agricultural seasons. They would return to Mexico in the winter, but the introduction of a hard border incentivized people to remain in the US.

It seems the hardening the border lead to the exact thing Harlan Crow and the other racist trash were trying to fight, increased immigration.

All immigration is a net positive to the economy in a number of different ways, and most of "problems" are caused by material conditions created by having classes of citizens versus non citizens. The US basically had open borders for much of its history and that's a big reason why it became such an industrial powerhouse.

The original idea behind physical border control has more to do with espionage and sabotage than restricting immigration.

What do you mean "how it works"? What function would 'having no borders' serve?