A society is defined as a shared system of values, beliefs, and attitudes that influence the perceptions and behaviors of its members. Societies form in order to provide mutual support for humans, who are inherently weak alone. The first societies consisted of small groups of 25 gatherer-hunters who banded together nomadically for protection and reduced conflict. As the last ice age ended around 12,000 BCE, tribes migrated to river valleys for food and began domesticating animals, irrigating fields, and developing more permanent settlements, chiefdoms, and early civilizations along the Tigris, Euphrates, Indus, Yellow, and Nile Rivers. Throughout history, societies developed class structures and governments, and faced conflicts