Bronze is a very useful alloy of copper and tin. It is stronger than most other metals, but inferior to steel. Early man learned how to use bronze to make better weapons and tools such as plowshares and pruning hooks as well as weapons such as spears and arrowheads during the Bronze Age.
In nature copper and tin are not normally found in the same area. (In antiquity, the British Isles were referred to as the "Tin Isles" whilst the name of the island of Cyprus has its roots in the word for "copper".) Consequently it is natural that as bronze became more important, centers had to become more organized; and as trade routes were opened up between the sites of the respective metals, technology and knowledge flowed between cultures, hastening the spread of civilization. It is not an accident that there are links between the advent of bronze working and the introduction of writing in many areas. In many places it enabled the introduction of the plow.