History is the study of the past, including the prehistory of man, all the way back until our origin in Africa about 200,000 years ago. Modern history is generally thought to begin in Classical Antiquity, around 800 BCE, when large numbers of scholars began to write things down. Herodotus of Halicarnassus (484 BCE – ca. 425 BCE) and Thucydides (ca. 460 BCE – ca. 400 BCE) are generally considered the "fathers of history," with the latter taking special care to use a scientific approach in the study of history, attributing major events to human choice rather than divine intervention.
Today, history forms a huge component of human knowledge in general, alongside cultural and scientific knowledge, both of which overlap with history. Historians place a great emphasis on primary sources; people writing based on events they or their immediate friends actually experienced, rather than secondary sources, writing merely based on hearsay. Also important are comparisons between primary sources — without comparisons, it can be difficult to validate historical claims. Obviously, the history of an invasion will be written differently by the conquerors and the conquered.
History is generally periodized into several broad strokes, to make it easier to analyze and understand. First is prehistory, extending over a couple hundred thousand years, from the beginning of humanity to the Neolithic Revolution, which began between 10,000 and 8,000 BCE. The Neolithic Revolution heralded the beginning of agriculture, the establishment of the first cities and non-agricultural classes.
Thousands of years after the Neolithic Revolution, various ancient civilizations were founded: Mesopotamia (5000 BCE), the Indus Valley Civilization (3300 BCE), ancient Egypt (3150 BCE), ancient China (3000 BCE), Minoan Crete (2700 BCE), Mycenaean Greece (1600 BCE), Kingdom of Israel (930 BCE), ancient Rome (900 BCE), and many others. Historians study these on a civilization-by-civilization basis, with objectivity as the primary goal.
The end of the era of ancient history is arbitrary, but the year 476 CE, when the Western Roman Empire fell, is often cited. Between 476 and around 1492 is the period of time known as the Middle Ages, while from 1492 to today is called the Modern Era. Modern history focuses mostly on the last 500 years.