1930s Germany didn't hate the japanese, despite them being very different from them (appearance, culture). Instead, they hated the German/european jews, who were basically visually indistinguishable.
it was a few that pushed that hatred. Hatred is usually engineered as a distraction for a crime. Usually those committing the crime and pushing the hatred are very close.
I feel like you're making the mistake that the governments represent the people here. The peace is between the people, not the governments, its the governments that want to fight and want to keep the people apart so they don't realise the peace.
If we all know someone everywhere in the world then how will our governments convince us to attack them if our friends live there?
I disagree, I think the tribalism is artificial and primarily bound the constraints of our ability to perceive reality due to our corporal form and its limitations. Fundamentally we're very empathetic but its all about being able to put the right information in front of the right people at the right time.
Its a matter of information logistics and applied correctly; people like people. Its when people quarantine information and selectively release it (e.g. only negative information) that tribalism can grow.