French Presidential Election

[Viking]

"I think a world composed of homogeneous nation states would be much more peaceful " Due to the number of civil wars we French had in the past, I am not sure of this.

Diverse countries have a lot of civil wars too (between majority factions, with separatism on top of this), and the odd genocide every now and then. I suspect that recent or current authoritarian rule could be a factor in many civil wars.

Russia

Very diverse; many relatively recent imperial acquisitions still under control.

Iran

Seemingly pretty diverse, also a theocracy.

North Korea

One of the most extreme dictatorships in history.

Not if there only was one country.

Then you could have larger ethnicities dominating smaller ones.

Who was the latter? Russia?

The Serb assassin.

And the Empires were quite homogeneous in terms of the makeup of the people who actually had a say in them.

Those other groups typically went for independence when they saw a chance, either with or without violence, instead of focusing on representation.

the population usually had no contacts or friends in the other group.

In typical democratic countries: a question of technology as much as anything else.

Even worse things happened in WW2 when the NSDAP began to declare an in-group and began to teach all kinds of stereotypes about those outside that group. And it wasn't just the jews, they said similar things about blacks, slavs, etc. The US also wasn't nice to the Japanese with all the mass internment and propaganda. Now they didn't start a war based on it, but they performed injustices based on these ideas. Gangs and many other social interactions work in a similar way.

You'll note that the 'worst' things typically were carried out by dictatorships.

EDIT: Also somewhat ironic to bring up the US, where the majority population consists of mixed immigrant populations. A new nation grew to replace the old ones.

Which may just as well just be a short term view once more, using more Co2 is also good for the money in the short term, doesn't mean it's wise to do it.

A strategy can be better than another both in the short and long term if the other strategy is sufficiently bad.