French Presidential Election

[Viking]

I think a world composed of homogeneous nation states would be much more peaceful than we world we currently have. A lot of rebellions have been started with the purpose of carving out or reclaiming space for a people that had no independence. Do you think the UK would have been better off if Ireland had not been granted complete independence? If Northern Ireland is anything to go by, it wouldn't.

Furthermore, force has many times been used with the purpose of adjusting borders according to ethnicity; the annexation of Sudetenland and the annexation of Crimea being relevant examples.

In sum, heterogeneity within countries has inspired a lot of violence and bad behaviour.

I don't see how a world of culturally homogeneous countries would make it easier for large and wealthy countries to dominate (if anything, some larger countries would get split up). Smaller countries would have to band together in order to be stronger when facing larger countries, but they do not need to have open borders with one another in order to accomplish this. If the EU had stuck with political and economical cooperation rather than gradually morphing into the USE, it may had been in a much better/more stable state today.

the goal needs to be to break up cultural barriers and mix people up more and more

Yet that's not always realistically achievable in the near to medium term (or even long term), and naturally gets more difficult the more immigrants are settled.