The Mauryan Empire was the first power to unite most of the Indian subcontinent, and at its peak stretched from Afghanistan in the north-west, east almost to the mouth of the Ganges and south as far as modern Mysore. The Empire was founded by Chandragupta Maurya, the first great conqueror in Indian history, and expanded by his son Bindusara, and grandson Ashoka, before declining rapidly under Ashoka's successors and disappearing by around 185 BC.
The Mauryan Empire was built around the kingdom of Magadha, an important early Indian state that owed its prosperity to its position on the trade routes on the Ganges. Magadha has expanded under earlier dynasties, and under the Nanda dynasty controlled most of the Gangeric Plain.
Two different traditions survive about the origins of Chandragupta, portraying him as either a lowly-born relative of the Nanda family, the son of Mura (thus Maurya), or as a member of a nomadic Himalayan tribe, the Mauryas. He entered service with the last of the Nandas, and became his commander-in-chief, before leading a first unsuccessful revolt and being forced into exile. While in exile he met with Alexander the Great, then campaigning in the Punjab, and is said to have learnt about military matters from the great conqueror.
Alexander left India in 325 BC, leaving weakly held provinces in Sind and the Punjab. Alexander's death in 323 BC removed any chance that these provinces would remain part of the Macedonian Empire. In 321 BC, in the second partition of Alexander's empire, the Indian kings Poros and Ambhi were appointed to command the Indus valley and the Punjab, while Peithon, Satrap of the Indus Delta, was moved to Arachosia, on the western side of the river. It is also at about this date that Chandragupta overthrew the Nanda dynasty, possibly with the help of Poros. Over the next few years he gained control of the Punjab and Sind, taking his empire up to the Indus. The Macedonians returned in around 303 BC, when Seleucus Nicator appeared on the Indus in an attempt to regain control of the eastern part of the old Persian empire. Although this campaign ended without a major battle Seleucus was willing to exchange his remaining provinces west of the Indus (reaching into the Kabul valley) for 500 elephants (see Seleucus Nicator's Invasion of India).
Towards the end of his life Chandragupta is said to have converted to Jainism, and eventually to have fasted to death after a famine struck his empire. He was succeeded by his son Bindusara, whose reign is very obscure. At some point before Bindusara's death in c.273 BC either he or his father expanded the empire into the Deccan, leaving only the southern tip of the sub-continent and part of the east coast outside their control.
The Empire expanded one final time under Ashoka, Chandragupta's grandson. He conquered the coastal kingdom of Kalinga (c.271-261 BC), but was so horrified by the human cost of the war that he renounced aggressive war. Ashoka's vigilance and energy meant that the Empire survived intact throughout the rest of his reign and the army continued to exist and to take part in defensive campaign, but his successors were less able. The Empire came under pressure from the north-west, from the Bactrian-Hellenic kingdom, while some of its component parts split away. The Empire may even have split in two, in around 185 BC the last Emperor of the dynasty, Brihadratha, was killed by his commander-in-chief Pushyamitra, founder of the Shunga dynasty.