From Harari's 21 Lessons for the 21st Century, on p. 111-26 of my copy:
... For hundreds of thousands of years Homo sapiens and its hominid ancestors lived in small intimate communities numbering no more than a few dozen people. Humans easily develop loyalty to small intimate groups such as a tribe, an infantry company or a family business, but it is hardly natural for humans to be loyal to millions of utter strangers. Such mass loyalties have appeared only in the last few thousand years – yesterday morning, in evolutionary terms – and they require immense efforts of social construction.
People went to the trouble of constructing national collectives because they confronted challenges that could not be solved by any single tribe. Take, for example, the ancient tribes that lived along the Nile River thousands of years ago. The river was their lifeblood. It watered their fields and carried their commerce. But it was an unpredictable ally. Too little rain – and people starved to death; too much rain – and the river overflowed its banks and destroyed entire villages. No tribe could solve this problem by itself, because each tribe commanded only a small section of the river and could mobilize no more than a few hundred laborers. Only a common effort to build huge dams and dig hundreds of kilometers of canals could hope to restrain and harness the mighty river. This was one of the reasons why the tribes gradually coalesced into a single nation...
In previous centuries national identities were forged because humans faced problems and opportunities that were far beyond the scope of local tribes, and that only countrywide cooperation could hope to handle. In the twenty-first century, nations find themselves in the same situation as the old tribes: they are no longer the right framework to manage the most important challenges of the age. We need a new global identity because national institutions are incapable of handling a set of unprecedented global predicaments.
We now have a global ecology, a global economy and a global science – but we are still stuck with only national politics. This mismatch prevents the political system from effectively countering our main problems. To have effective politics, we must either de-globalize the ecology, the economy and the march of science – or we must globalize our politics. Since it is impossible to de-globalize the ecology and the march of science, and since the cost of de-globalizing the economy would probably be prohibitive, the only real solution is to globalize politics. This does not mean establishing a global government – a doubtful and unrealistic vision. Rather, to globalize politics means that political dynamics within countries and even cities should give far more weight to global problems and interests.