This chapter first theorizes as if each system leader has been similar in terms of the resource foundations it has brought to the arena and what it has been able to do with those foundations. Earlier leaders were much weaker than later leaders. What accounts for the difference? Our answer is that system leaders have had variable claims to leads in commerce, technology, and energy. When they combined all three, they became very powerful. The chapter then addresses one of the central issues of Big History: the swinging of the socioeconomic, military, and political lead from western Eurasia to eastern Eurasia and back to western Eurasia and North America in what is sometimes referred to as the “Great Divergence.” This oscillation was put in motion by the discovery of agricultural techniques that gave the West a lead to innovate all sorts of things. Gradually the East caught up, until at one point Rome and Han China were roughly equal. After Rome declined and the Han Empire fragmented, China came back in the Sui–Tang–Song dynasty period, while western Europe remained fragmented. However, the medieval Chinese lead did not persist. Ultimately, the West was able to forge ahead by combining new energy sources and technology. Now, China may be catching up once again.