The development of writing and, consequently, written records, is a major dividing point in the history of a race of people. The period before the development of writing is termed prehistory; the period after writing develops is called recorded history. The study of prehistory relies solely on tools, artifacts, art and other such remnants of daily life. The study of recorded history draws heavily on written records, though tools, art and architecture are still important.
Tools are an integral part of human history, so it is not unexpected that historians often divide historical periods based on the tools in use at the time. The Stone Age encompasses the period when humans used stone tools such as flint axes and obsidian knives. The Age of Metal marks the discovery and use of smelting to make metal tools, and is further subdivided into the Bronze Age and the Iron Age.
Historians also have made a distinction between ancient history and modern history, though the division point has changed over time. Traditionally, ancient history described the period up until the fall of the Roman Empire, with modern history covering everything since then. In the 21st century, historians generally add a third period, the Medieval period or Middle Ages, covering the time from the fall of the Roman Empire to the end of the Renaissance and the beginning of the Age of Discovery.
History can be divided based on geography as well as time period. Because divisions based on the advent of writing, the type of tools used or the rise and fall of individual empires may have different timelines or limited relevance outside of a given area, historians may divide the subject into American history, European history, Chinese history and the like. Dividing history in this way facilitates academic specialization and reduces the tendency to focus on one part of the world to the exclusion of others.