What we have seen is that EU-Europe has after hundreds of years of war now has a long period of stability. We see that it also has an effective EU-wide political moderation system for common values.
> As a non-EU country, they can instead undermine EU policy (ie: lower taxes, cut standards, etc..) in order to attract companies (near-shoring).
Taxes are not EU-wide regulated. Near-shoring is much easier INSIDE the EU - being a near-shore offering company is inside the common market MASSIVELY simpler. That's for example why many German companies build factories in neighboring countries. Countries geographically/economically next to the EU, but not inside the EU, are still under massive influence. Before the EU, most European countries synchronized their currency with the German DM (Deutsche Mark). There was also a monetary mechanism to do that. Basically the German central bank dictated much of the currency policy in EU, more or less indirectly. Nowadays that power has been delegated to the European central bank, where the German influence is reduced.
> The US will be happy to see the EU crash into a thousands easily manipulated city-states than the current status quo.
Not at all. Maybe the populist right of the republicans. Other than those, both Republicans and Democrats see the EU and its member states as allies.
> the Russian threat for now which justifies the existence of the EU
The Russian threat justifies the existence of NATO. The EU has an independent justification of its existence. The existence of the EU is a threat to the Russian system, since it exposes its lack of freedom and lack of prosperity of its people.
> We can’t know for sure if the EU is preventing war. Smaller countries might think the EU is not serving them well and revolt. Germany might flip and decide to invade the other countries again. ... There is no reason or proofs that suggests it can’t happen again.
We can't prove anything about politics, if you mean 'prove like mathematical theorems', but we are hardly completely in the dark. Nothing like what you describe has ever happened in any mature democracy, as far as I know.
> A country like croatia might benefit more from being not into the EU.
You can type 'might', but what does it mean? I might win the lottery. Putin might become a Quaker and reject war. Who knows?
2. This is over-generalizing. A country like croatia might benefit more from being not into the EU. As an EU country they have to play by EU rules and standards. As a non-EU country, they can instead undermine EU policy (ie: lower taxes, cut standards, etc..) in order to attract companies (near-shoring).
> Without the EU as an ally, the US may be too small to compete.
The EU needs the US more than the US needs the EU. People who think the US is an ally to the EU are delusional. The US is undermining the EU to reduce its power and to reduce its dependency to it. The US will be happy to see the EU crash into a thousands easily manipulated city-states than the current status quo. Of course, there is the Russian threat for now which justifies the existence of the EU. But they are working on that (at the expense of the EU of course).