As we have seen, various factors such as climate, topography, and disease made India very difficult to unify. By the same token, we have also seen how India's religious and philosophical ideas were flexible enough to act as a unifying influence. After 400 BC, the combination of these opposing influences has allowed a succession of states to unify India briefly, only to come apart again.
The first empire of note was that of the Mauryan Dynasty. Its founder, Chandragupta Maurya (325-299 B.C.E.), was the ruler of Maghada, then the largest state in northeastern India. By 315 B.C.E. he had expanded into the Punjab and Indus River valley where he clashed with the Macedonian general, Seleucus. Being preoccupied with the struggles for power following Alexander the Great's death, Seleucus surrendered his Indian lands to Chandragupta in return for 500 war elephants. (Those elephants would play a crucial role in the battle of Ipsus and the subsequent emergence of the Hellenistic Kingdoms).
Chandragupta and his son, Bindusara, extended Mauryan rule over northern India and the Deccan to the south. Their rule was strict, reputedly having an army of some 700,000 men and 9,000 elephants. In the words of the Arthashastra, the political manual written for Chandragupta, "Government is the science of punishment." On the other hand, also following the Arthashastra's advice that a king's good is what is good for his subjects, Chandragupta and Bindusara built and maintained roads, bridges, and irrigation systems.
Bindusara's successor and one of the most remarkable rulers in history was Ashoka (269-232 B.C.E). A bloody struggle for the throne and the even bloodier conquest of Kalinga in 261 B.C.E upset him so much that he embraced the Buddhist concept of non-violence and renounced war, gave up the hunt, and outlawed the killing of any animals not used or eaten. Throughout his reign, Ashoka continued to rule in the spirit of Buddhism (which he may also have seen as a unifying force for his empire). He sent out officers of righteousness to ensure the just rule by his officials. He codified Buddhist laws and principles. And he worked for the welfare of his subjects by digging wells, building rest houses and planting banyan trees for shade, medicinal herbs, and mango trees. Unfortunately, Ashoka’s policy of non-violence also undermined his army's efficiency, which allowed revolts, invasions, and the fall of the Mauryan Empire by 185 B.C.E.
The fall of the Mauryan Empire allowed the expansion of the Greek kingdom of Bactria (modern Afghanistan) into northwestern India around 150 B.C.E. The Greeks probably influenced Indian culture in a number of fields: medicine, astrology, drama, and sculpture. There is even a philosophical work, The Menander, where the Greco-Bactrian king, Menander has a dialogue with a Buddhist monk.
From about 50 B.C.E to 78 C.E. a succession of Asiatic tribes pushed into northwestern India. One of these tribes, the Kushans, united the others behind them and established a kingdom that encompassed northern India from the Indus to the Ganges valleys and possibly to the Himalayas and the Silk Road. This period also saw the rising influence of a middle class of merchants and craftsmen who took full advantage of their central position for trade. Therefore, the Kushan capital of Purashapura in the rich province of Gandhara became the hub of a lively trade between Rome, India, and China. Indian merchants especially profited from their middleman role of getting spices from South-east Asia and silk from China for Roman traders. The large number of Roman coins circulating in India at this time indicates how extensive and profitable this trade was for India and likewise how costly it was for Rome, being one of the causes for its decline and fall.
India exported and imported more than material goods at this time. Buddhism was especially popular with Indian merchants, since it was one occupation that could stay clear of killing people, animals, and even small creatures in the soil. As a result, merchants spread Buddhism to Southeast and Central Asia and as far away as China. Indian culture was so influential in the emergence of civilization and kingdoms in Southeast Asia that this region along with India has been referred to as Greater India. Buddhist ideas may have even influenced such religious groups in the Roman Empire as the Manicheans, Gnostics, and Neo-Platonists.
By the same token, foreign ideas also influenced India. Greek influence was seen in the Gandharan style of sculpture, which portrayed Buddha with curly hair and made its way as Far East as China. Also the Kushan rulers adopted the Chinese title "Son of Heaven." Even more striking was the influence Christianity might have had on Buddhism, in particular the idea of Maitreya Buddha, the suffering savior who would redeem us through his own pain.
Although Buddha himself had resisted any attempts to deify him, such attempts started soon after his death. By the first century C.E., this had created a split in Buddhism. The old belief of each of us being responsible for our own salvation was known as Hinyana Buddhism ("the Lesser Vehicle") since we each must strive for salvation on our own. The newer belief was called Mahayana ("the Greater Vehicle") since Buddha saves all of us together. One spin-off of this idea was that of the Bodhisattvas, people who have earned Nirvana but have chosen to stay behind in this world to help other people attain Nirvana. Over time, various branches of Mahayana would emerge, some having innumerable Bodhisattvas inhabiting complex hierarchies of heavens as stages leading to Nirvana. Hinyana Buddhism would be the dominant form of Buddhism in Sri Lanka, Burma, and Southeast Asia. Mahayana would prevail in India, Central Asia, Tibet, China, and Japan.
The Kushan realm remained a center of culture until its demise in the late third century at the hands of a new power rising in the West, the Sassanid Persians. However, a new native dynasty, the Guptas, emerged in the fourth century to take the Kushans' place. Its founder, Chandra Gupta I (319-335), although from an obscure family in Bihar in the northeast, made a favorable marriage that helped him control the Ganges River Valley by his death. His successors eventually brought Northern India under their rule while states in the Deccan and Sri Lanka agreed to become the Guptas' vassals.
The Gupta period is seen as a golden age of Indian culture. Indian astronomers came up with the idea of a round earth rotating on its axis. Indian mathematicians developed such concepts as Pi, negative numbers, a decimal system with place value digits, zero, and quadratic equations. Unfortunately, these ideas remained the preserve of a select group of individuals. Not until the Arabs came into India and adapted these concepts for their own uses were they made generally available. This is reflected by our still referring to them as Arabic numerals. In literature, India's two greatest epic poems, the Ramayana, and Mahabharata, which itself contains possibly the most revered work in Indian literature, the Bhagavad Gita, were written down in their final forms. India's greatest playwright, Kalidasa, flourished at this time. Unlike Greek drama, the point of Indian drama is to delight the audience and leave it with a serene and peaceful feeling. Both Buddhist and the emerging Hindu art and architecture also thrived. Once again, Greek influence can still be seen in the simplicity and serenity of Buddhist art. Hindu temples were modeled after caves, which Indians always considered sacred and were decorated with sculptures.
During this time, a major shift took place in the religious climate of India. The Guptas, like many rulers before them, had been active supporters of Buddhism. This, and their popularity among the rich middle classes, led to large contributions to Buddhist monasteries, which became quite wealthy, much like their counterparts in Christian Europe. Besides theological disputes and the corruption such wealth and influence at court might bring, Buddhists tended to move their monasteries away from populated areas. Meanwhile, the Brahmins were renewing contact with the people and winning many converts to their religion, which at this point had evolved into what we now call Hinduism. In the following centuries, Hinduism would replace Buddhism as the major religion in India, although it continued to spread across Asia.
Of the world's great religions, Hinduism is especially unique, since it has no historical founder who had some revelation at some point in time. It has no fixed set of worship, with some people praying, others making sacrifices, and still others meditating. Although it is polytheistic, recognizing millions of gods, it is somewhat monotheistic in that it sees these various gods as manifestations of the one unifying god, Brahma. It is this flexibility that has made it so popular and such a unifying force in India.
While there are millions of gods, there are three that most people worship one or the other of: Brahma, Vishnu, and Shiva. Brahma is seen as the supreme being of creation who put into motion a constantly repeating cycle of destruction and rebirth. Although seen as the supreme god, who all others are reconciled to, Brahma has not been as popular as Vishnu and Shiva. Vishnu is the kind and merciful preserver of Brahma's creation who has appeared in various manifestations, known as avatars, to help humanity. The most popular of his manifestations has been Krishna, who as a child was full of mischief and as an adult a great lover and a mighty warrior, qualities once associated with Indra. Shiva combined the attributes of various Harappan and Aryan gods, being at once a god of destruction and rebirth, mercy and wrath, and constancy and unpredictability.
Hinduism maintains the old Brahmanic and Buddhist principles of karma, dharma, and reincarnation. Unlike the old Brahmanic religion, it puts more emphasis on personal devotion to a god than on sacrifices performed by the Brahmans. This made Hinduism especially popular in India and it has dominated India ever since. However, the coming of Islam in the eighth century offered a new challenge to Hinduism's dominance.