It's often perplexing to note how violent human existence has been. Until the end of world wars, it was common for armies to be raised and sent to die. Only when institutions like trading, finance and learning, which do not occur optimally in turmoil, spread worldwide, there was an incentive to keep peace. This leaves us with a question as to why peace wasn't pursued over the early years of human civilisation.
The answer to that would be science or, to be more specific, maths. Before maths, most languages were subjective and interpretive rather than definite and logical. With that power of subjectivity, it was easy to evade having to answer. How big is the earth, you ask? While under maths, you will have to put units, and then under physics, estimate and verify it; in any other language, you can just have a word for it. Subjectivity gives an illusion of an answer, preventing one from digging further and, in this case, striving to learn more. That leaves us with a vacuum, which gets filled by faith - which has caused the biggest wars in humankind.
But ever since science began to spread, the sheer nature and repeatability of the experiments reduced uncertainty. They exposed the lack of completeness in our understanding of ourselves and the world. In fact, even in World War 1, armies fought on the backs of horses and cavaliers holding spears. But it quickly became clear that aeroplanes were a much better arsenal in the war. Therefore, industries were run on overdrive during the Second World War. But it is frightening. This led to a cognitive dissonance since industries were primarily a means of trade. Now that industries decided the outcome of wars, they had brought together war and trade, which were incompatible. From wars to colonies, all were efforts to increase wealth by capturing more resources, but they halted progress in trade. In fact, the realisation that trade was a substitute for war could be the greatest reckoning of humans. However, this came on the back of scientific opulence, which promised all basic necessities. Without the infrastructure to be included in trade, a war remains the only means to gain wealth.