The Indo-Europeans originated from the steppes north of the Caucasus Mountains and spoke forms of an ancestral Indo-European language. They migrated over 500 years for reasons like overgrazing or population growth. One group, the Hittites, occupied Anatolia around 2000 BC but were later conquered. Another group, the Aryans, crossed into India's Indus Valley and left sacred texts called the Vedas describing their pastoral life. The Aryans developed a caste system in India dividing people into priests, warriors, peasants/traders and laborers based on skin color and purity, with membership determining one's role and social interactions.