Trump likely to acknowledge Jerusalem as the Capital of Israel

[Viking]

What is your evidence that an ethno-state "increases the security of an ethnic group that possesses one"? Post-war Europe?

Superficially, it makes perfect sense that it would; so I would just as well look for things that would go against it, as I'd expect it to be true.

Obviously if there were no Jews in Europe in the 1930s, Hitler could not have killed them. That's not an argument for colonizing Jews (which Hitler endorsed in the '30s). If you don't have a minority to persecute, you can always manufacture one.

If the same or similar amount Jews were present in Europe in the early 1900s, and we also had a state of Israel created at some unspecified point earlier, then:

1. Hitler might forcefully deport all Jews to Israel
2. a large amount of Jews could migrate voluntarily in response to the deteriorating situation in Germany, making 1. a more likely outcome for the smaller group that still remains
3. the state of Israel might offer to resettle all German Jews, including footing the bill for the whole thing. For those that refuse to resettle, 1. can still be a later outcome (rather than death)
4. the state of Israel can alter the outcome in yet different ways: helping Jews escape occupied areas in different ways, like sabotage and other clandestine operations, maybe even strategic bombing raids once the war has started if they can get to any friendly airfields close enough; they may also use diplomacy to make the allies put more effort into stopping or reducing the extent of the Holocaust, both before and during the war, and so on

A thousand micro-states drawn on ethnic lines would not by virtue of borders offer security, because these would not have the strength to defend them, our transnational institutions would not exist, and most of these states would be gobbled up into the empires of the largest nations (or most powerful warlords) - as was standard practice in the pre-modern times.

Many or all of the larger nations would lose a lot of their territory and population if we started carving them up, and would be weakened.

Furthermore, small nations could form defensive pacts à la NATO. If one country buys one fighter jet, then 500 small nations is 500 fighter jets. This organisation leaves not a good fundament for independently projecting power (a single fighter jet makes no invasion), but for the given ethnic group, that's probably not worse on average compared to if they had formed a small part of a much larger country (and smaller groups of small individual countries can still agree to project power, obviously).

Nations are not eternal, for immigration to undermine some static measure of security or sovereignty. Wars between states are not driven by "third-party" immigration.

In the most basic forms, this is straight forward. If we have two approximate ethnostates A and B, and a huge chunk of people migrate from B to A to form 10% of the population there, then if B later (e.g 10 or 100 years) declares war on A, those 10% may leave A in a weaker position than A would have been without them, because of significant sympathies for B from these 10%. The result may be significant unrest (potentially even civil revolt in certain areas, if the ethnicities live largely separated), increased amounts of sabotage, or, even without much sympathy at all from the 10% towards B: severe trust issues among soldiers (potentially conscripts) and civilians.

You could also replace B with the approximate ethnostate C as the agressor, where C has the same religion as B, or some other connection, and thus can make a lot of the 10% feel sympathetic towards C. You can furthermore "replace sympathy to B" with "apathy", in either scenario, as well as in scenarios where ethnostate D has a beef with the ethnicity of A, but not B.

Note also with the loss of autonomy trough democracy that the majority will have, in the last paragraph; which could impact the security of the original population negatively, even if it remains the majority.

Unless you think fascists take over - but that's a problem with fascists, not with immigrants.

Yet if the indirect problem is easier to tackle than the direct one, tackling the indirect one can be the way to go. To say that something is "not really the problem" is only relevant for the solution as long as solving the "real problem" is feasible and desirable (given potential downsides).

Ethnic majorities in non-imperial context almost by definition have the majority of institutional power and resources, but devolution has been and clearly still is a controversial subject. Nevertheless devolving powers to minorities does not reduce the sovereignty of majorities, unless by sovereignty you mean domination. Which would have to bolster the arguments for transferring some power to minorities. Your position seems very different, therefore, from one who believes that nations should submit to centralized political unions because of mutual protections and benefits...

If the immigration is large enough for long enough, the minorities will become the new majority. Long before that point, they will also have a large power potential in democracies: if 10% of the population was from a certain immigrant background and most of them voted in a distinct fashion, that can mean a lot influence in a democracy and reduce the autonomy, or whatever you want to call it, of the original population relative to that it would have had without the immigration.