Short answers, pulled from the story.
A civilization is any complex society characterized by the development of the state, social stratification, urbanization, and standardized symbolic systems of communication such as writing. As the National Geographic Society explains, the most basic definition is a society made up of cities. The word relates to the Latin civitas, meaning city.
Mesopotamia hosts the earliest civilizations, developing from 7,400 years ago, with the Neolithic Revolution beginning in West Asia. The Natufian culture in the Levantine corridor planted cereal crops from about 11,000 BCE, and Neolithic life took hold at sites like Göbekli Tepe from around 9,130 BCE. Independent neolithic revolutions also began from 7,000 BCE in northwestern South America and Mesoamerica.
Research from the Journal of Political Economy argues that cereal farming produced civilization because of the appropriability of the yearly harvest, even though horticultural gardening was more productive. A grain harvest could be taxed, which sustained a taxing elite and urban development. Highly productive roots and tubers were a curse of plenty that prevented the emergence of states.
Adam Ferguson is credited with the first use in English, writing in his 1767 Essay on the History of Civil Society that the species advances from rudeness to civilisation. The abstract noun arrived in the 1760s from French, with the first French use traced to 1757 by Victor de Riqueti, marquis de Mirabeau.
Theories range across historical and general models. Edward Gibbon blamed immoderate greatness for Rome, Joseph Tainter pointed to diminishing returns to complexity, and Jared Diamond's 2005 book Collapse named environmental damage, climate change, trade dependence, and violence across 41 studied cultures. Arnold J. Toynbee blamed the failure of a creative minority, and Peter Turchin modeled fiscal-demographic cycles ending in famine and state breakdown.
The Kardashev scale classifies civilizations by their level of technological advancement, measured by the amount of energy a civilization can harness. It is hypothetical and places energy consumption in a cosmic perspective, making provisions for civilizations far more advanced than any known to exist. An alternative view suggests future civilizations may pursue technological minimalism and extreme miniaturization instead of ever-increasing energy use.