The Indus Valley Civilization is the oldest civilization we have record of in India. The Indus Valley was significant because of the presence of the Indus River, which, like the Nile in Egypt, had very predictable semi-annual floods, which ensured a steady agricultural base.
One of the earliest Indus Valley societies are the Harappa, which existed between 3000-1700 BCE. They had a thriving agricultural society that also engendered a strong trade base within the region until they began to fade out after about 2000 BCE.
During that time, the Indus Valley was home to a vibrant network of trade, with denizens trading grains, livestock, and tools within the valley, as well as as far away as Mesopotamia. Of particular note are the Harappan square seals, frequently carved with intricate designs as seen above. They were thought to be part of a writing system, possibly as an indication of maker or place of origin.
After 2000 BCE, the Harappan society suffered a decline. Most theories indicate that there was a shift of the rivers in the Indus Valley, which caused croplands to become less fertile. Eventually, for whatever reason, people moved away from the Harappan cities, and by 1700 BCE, the Harappan civilization had all but vanished.
Around 1500 BCE, a group of nomads moved into the Indus valley from the north, blending their own culture with that of the indigenous people of the valley, producing some political conflicts but also stabilizing the region.
Eventually, the Aryan culture prevailed, and began propagating. Based on the Vedas, ritualistic hymns composed by Aryan priests, the culture involved a strong love of music and celebration, games, as well as war. Eventually, however, like a melting pot, Vedic culture began to take on ideals from those it assimilated.
Chief perhaps among these ideals was the concept of varnas, classes of society based on the functions of its people, with Brahmins (priests) at the top and Shudra (conquered peoples used for labor) at the bottom. This system lent itself very well to cultural stability, especially when coupled with the religious belief that performing one's role in society would lead to reincarnation into a better life.
Lowest of all, however, were those who dealt with objects believed to be 'unclean', such as human or animal waste, or the disposal of corpses. It was believed that such things brought spiritual pollution, and thus they were considered 'untouchable', for fear of their spiritual uncleanliness spreading by contact.
Changes came, however, when a prince named Siddhartha Gautama chose to eschew his lavish lifestyle in favor of a more ascetic one, teaching others to follow his example and eschew desire in exchange for inner peace. He came to be known as 'Buddha' (Enlightened One), founding a religion that proved to be very popular among the 'unfortunate' people on the bottom of India's caste system because it taught that the path to their salvation lay not in performing their assigned role and hoping for the best, but rather in eschewing material desires and seeking a perfection of the self.
One of the more famous early followers of Buddhism was Ashoka, who took over India in a bloody war that caused him to become sickened by violence and seek a more nonviolent path. As a ruler, he preached nonviolence to his people and spent many resources on improving the lives of the populace, constructing wells, hospitals, and irrigation systems. He also preached religious tolerance, unusual for the time. Sadly, his successors lacked his kindness and ability as a leader, and Ashoka's empire fell to pieces shortly after his death, leaving the region in disrepair and disorganization for centuries to come.