[quote=@Vilageidiotx]

So if it is about resource acquisition or conquest, locals will get hurt. If it is about getting the other side to acquiesce, then it might just end up being terrorism that becomes the main way to wage war. 
[/quote]

We could bring this around to the present day as something to consider when looking ahead into the future. Wikipedia cites White, Philip L's "Globalization and the Mythology of the Nation State" when it says that in the post-Cold War era (or perhaps even as a personal addition: the post-WW2 era) that the existence of validity of a nation-state it much more defined by multi-national agreements and super-pacts between nations than the old world idea that a nation-state often derives validity on the people it rules (and aligned to the people it rules) with a national mythos that back up their own rule. But we have now in the world a political landscape with nations that don't define a single ethnic group but may arbitrarily encompass several, or divide existing ones (the African nations, the Arab world) and that these countries don't obtain their own validity by a shared heritage with its own people (either with two many once-feuding groups too scattered about the land to validate an ethnically-built nation-state or in the Arab world all the Arab peoples spread among dozens of nations and a national mythology speaks to a more pan-Arab ideology than a national ideology) but from other nations (Russia backing Syria, US backing Isreal, no one backing Palestine).

Wikiped than goes on to mention the growth of NGOs and international companies can erode the validity of a nation by providing the services the country could or should provide by themselves through outside funding, either with state-based patronage or private patronage. We could argue that with non-national entities like that the private individual could have more power over international problems than they had in the past with growing technologies and an infrastructure that supports a more robust industry that can bypass laws to do more than what we could have done in the past.

On top of that, I could make the independent argument that migrations mix and spread the once important ethnicities the old nations were built on that build multi-ethnic nations like the US or (supposedly) western Europe (though I tack on to this recognition this can be argued since I look at Europe now and still see a lot of fighting over the French/British/whatever identity native to their respective countries, where as the US may begrudgingly accept that the only natives are the people we genocided and that we're built on the premise of accepting immigrants).

Expanding: if trends like those Daesh are perfecting continue than we may very well see the end of war between nations but the war between abstract ideology. We won't be able to identify our enemies readily as we did in the past. This could change when the human race finds its first sapient sample of extra-terrestrial life and we someday go to war with it for some reason or another. But we could argue modern threats now are not bound to any one nation but can threaten them all, where ever they have ears and eyes that'll pay attention to them and believe in it.