Capitalism is the logical continuation of previous western economic orders, such as mercantilism and colonialism. But while the wealth generated by previous orders was derived chiefly from external sources, such as colonies, capitalism started using as economic fuel something which was available everywhere, in practically limitless supply: labor. Instead of going on expensive trips abroad to get slaves, or to milk foreign lands from their resources, wealthy investors could just hire the countless people lying around Europe, being increasingly left without anything to do by mechanization and technological advancements. They were willing to work for little money, which allowed industrialists to reinvest their profits in more mechanization, which allowed productivity to increase exponentially