Part 1: Pre-History vs. Ancient History
Part 2: Medieval History vs. Ancient History
Is ancient history anything that happened before your parents' time? Is it anything that happened before the period covered by your country's history? Is it the time before people started speaking the modern languages?
While these definitions may be valid in certain contexts, Ancient/Classical History at About.com uses a different set of criteria. This article contrasts the ancient period of history with
• the period of human life that came before (i.e., prehistory [a term coined, in English, by Daniel Wilson (1816-92), according to Barry Cunliffe (Britain Begins; Oxford: 2013)]) and
• the one that came after (the Middle Ages).
Meaning of History
You also need to understand what we mean by the seemingly obvious word 'history'.
Like most abstract terms, pre-history means different things to different people. For some it means the time before civilization. That's fine, as far as it goes, but it does not get at an essential difference between pre-history and ancient history.
For a civilization to have a history, it must have left written records, according to a very literal definition of the word 'history.' "History" comes from the Greek for 'inquiry' and it came to mean a written account of events.
Although Herodotus, the Father of History, wrote about societies other than his own, in general, a society has a history if it provides its own written record. This requires the culture to have a system of writing and people schooled in the written language. In early ancient cultures, few people had the ability to write. It wasn't a question of learning to manipulate a pen to form 26 squiggles with consistency -- at least until the invention of the alphabet. Even today, some languages use scripts that take years to learn to write well. The needs of feeding and defending a population require training in areas other than penmanship. Although there were certainly Greek and Roman soldiers who could write and fight, earlier on, those ancients who could write tended to be connected with a priestly class. It follows that much ancient writing is connected with that which was religious or holy.
People can devote their entire lives to serving their god(s) or their god(s) in human form. The Egyptian pharaoh was the reincarnation of the god Horus, and the term we use for their picture writing, hieroglyphs, means holy writing (lit. 'carving'). Kings also employed scribes to record their deeds, especially ones that redounded to their glory -- like military conquests. Such writing can be seen on monuments, like stele inscribed with cuneiform.
Archaeology and Pre-history
Those people (and plants and animals) who lived before the invention of writing are, by this definition, prehistoric. Prehistory goes back to the beginning of life or time or the Earth. The area of pre-history is the domain of academic fields with the Greek form arche- 'beginning' or paleo- 'old' attached. Thus, there are fields like archaeology, paleobotany, and paleontology (dealing with the time before people) that look at the world from before the development of writing. As an adjective, prehistoric tends to mean before urban civilization, or simply, uncivilized. Again, prehistoric civilizations tend to be those without written records.
Archaeology and Ancient History
These are working definitions. Classicist Paul MacKendrick published The Mute Stones Speak in 1960. In this and its follow-up two years later, The Greek Stones Speak, he used the non-written findings of archaeologists to help write history. (The first was a history of the Italian peninsula, and the second, which used results of the excavations of Troy conducted by Heinrich Schliemann, a history of the Hellenic world.) Archaeologists of the early civilizations often rely on the same materials as historians. Both take note of artifacts that survive the elements, like ones made from metal or pottery (but unlike most clothing and wooden products that decay in most environments). Underground burial sites may contain and protect objects that would have been used in life. Housing and those structures deemed ceremonial fill in more gaps. All these can corroborate the written information, should it exist at the time.
Different Cultures, Different Timelines
The dividing line between pre-history and ancient history also varies across the globe. The ancient historic period of Egypt and Sumer started about 3100; perhaps a couple of hundred years later writing began in the Indus Valley. Somewhat later (c. 1650) were the Minoans whose Linear A has not yet been deciphered. Earlier, in 2200, there was a hieroglyphic language in Crete. String writing in Mesoamerica began about 2600 B.C. That we may not be able to translate and make use of the writing is a problem of historians, and would be a worse one if they refused to avail themselves of the non-written evidence. However, by using the pre-literate material, and contributions from other disciplines, especially archaeology, the boundary between prehistory and history is now fluid.