According to Harari, money, empires, and religion led to widespread cooperation around the globe. Money led to a form of trust. In particular, it was able to cross cultural, political, and geographic barriers. In order to cooperate via money, people need only trust the monetary system of a trading partner and not the partner themselves. Empires, by contrast unified people through violence and culture. Violence is an ever-present feature of empires and is partly responsible for unifying cultures. The conquered cultures are often erased. However, this is not an entirely violent process according to Harari. He shows how conquered peoples in India took on new industries like tea farming based on the British desire to drink tea. The conquered Germanic peoples merged their culture with Roman culture over time. Even though Germanic tribes eventually destroyed Rome, Roman cultural artefacts remained. Religion is another unifying force. Specifically, the belief in a super-human power and inviolable standards and rules united peoples of differing beliefs. Missionary Religions brought people together (and contributed to empire-level wars) by bringing common customs and beliefs that are not specific to small local areas.
Harari speaks of the lack of determinism in history. It is worth studying history partly to see that the evolution of events is not inevitable. Other events, empires, religions, or cultures might well have dominated. Studying history carefully shows that human events unfold without regard to what is best. The study of the history of technology is a subset of the study of history and tells us the same things but with a focus on technology and science.