"Civilization" is a somewhat vague term that encompasses several interrelated human cultural trends: agriculture characterized by the domestication of plants and animals, making possible cities, and new forms of complex social structure therein. Prior to cities and civilization, humans were largely nomadic, following animal herds, in tribal groups of 100-200 individuals.
Civilization began about 12-10 thousand years ago, around 10-8 thousand BC, when the Pleistocene was ending and the Holocene was beginning. The Wisconsin glaciation, where permanent ice caps covered major portions of Europe, North America, and Asia, was ending, and the global average temperature was climbing to a more tolerable level. The selective planting of seeds was causing human-directed selection on plant species, making possible modern cereals like barley, lentils, and oats. These were highly modified from their wild precursors, with a greater caloric content and pleasant taste.
The first signs of human civilization are found in the Middle East and Egypt, most famously the Fertile Crescent, in modern-day Iraq. The first known city, Jericho, is located in the Jordan Rift Valley, in the modern-day West Bank. Evidence of a pottery industry, granaries, the domestication of animals, permanent settlements, and complex social structures with class systems have been found. The stationary nature of such settlements allowed for the accrual of personal possessions and the construction of fortifications for defense, with numerous social consequences that remain with us today.
There are several reasons why agriculture and civilization first developed in the Fertile Crescent. The area had significant geographical variation, making available many plant species for experimentation. The long dry season, and quick but relatively predictable rainy season contributed to the ease of plant cultivation. After crop yields were good enough that the nomadic lifestyle could be abandoned, true civilization, and all its trappings, was relatively quick to emerge.
Sheep, goats, cows, and pigs were among the first animals to be domesticated. Besides being used directly as sources of meat, milk, and leather, animals were used for their manure, whose high nitrogen content was ideal as a fertilizer.