of history in the early modern period and our contemporary period. Another early modern historian was Adam Ferguson. Ferguson's main contribution to the study of world history was his An Essay on the History of Civil Society (1767). According to Ferguson, world history was a combination of two forms of history. One was natural history; the aspects of our world which God created. The other, which was more revolutionary, was social history. For him, social history was the progress humans made towards fulfilling God's plan for humanity. He believed that progress, which could be achieved through individuals pursuing commercial success, would bring us closer to a perfect society; but we would never reach one. However, he also theorized that complete dedication to commercial success could lead to societal collapses—like what happened in Rome—because people would lose morality. Through this lens, Ferguson viewed world history as humanity's struggle to reach an ideal society. Henry Home, Lord Kames was a philosopher during the Enlightenment and contributed to the study of world history. In his major historical work, Sketches on the History of Man, Kames outlined the four stages of human history which he observed. The first and most primitive stage was small hunter-gatherer groups. Then, to form larger groups, humans transitioned into the second stage when they began to domesticate animals. The third stage was the development of agriculture. This new technology established trade and higher levels of cooperation amongst sizable groups of people. With the gathering of people into agricultural villages, laws and social obligations needed to be developed so a form of order could be maintained. The fourth, and final stage, involved humans moving into market towns and seaports where agriculture was not the focus. Instead, commerce and other forms of labor arouse in a society. By defining the stages of human history, Homes influenced his successors. He also contributed to the development of other studies such as sociology and anthropology. The Marxist theory of historical materialism claims the history of the world is fundamentally determined by the material conditions at any given time – in other words, the relationships which people have with each other to fulfil basic needs such as feeding, clothing and housing themselves and their families. Overall, Marx and Engels claimed to have identified five successive stages of the development of these material conditions in Western Europe. The theory divides the history of the world into