http://en.wikipedia.org/wiki/Ashoka#Embrace_of_Buddhism
Conquest of Kalinga
Fragment of the 6th Pillar Edicts of Ashoka (238 BCE), in Brahmi, sandstones. British Museum.The early part of Ashoka's reign was apparently quite bloodthirsty. Ashoka was constantly on the war campaign, conquering territory after territory and significantly expanding the already large Mauryan empire and adding to his wealth. His last conquest was the state of Kalinga on the east coast of India in the present-day state of Orissa. Kalinga prided itself on its sovereignty and democracy; with its monarchical-parliamentary democracy, it was quite an exception in ancient Bharata, as there existed the concept of Rajdharma, meaning the duty of the rulers, which was intrinsically entwined with the concept of bravery and Kshatriya dharma.
The pretext for the start of the Kalinga War (265 BC or 263 BC) is uncertain. One of Ashoka's brothers - and probably a supporter of Susima - might have fled to Kalinga and found official refuge there. This enraged Ashoka immensely. He was advised by his ministers to attack Kalinga for this act of treachery. Ashoka then asked Kalinga's royalty to submit before his supremacy. When they defied this diktat, Ashoka sent one of his generals to Kalinga to make them submit.
The general and his forces were, however, completely routed through the skilled tactics of Kalinga's commander-in-chief. Ashoka, baffled by this defeat, attacked with the greatest invasion ever recorded in Indian history until then. Kalinga put up a stiff resistance, but they were no match for Ashoka's powerful armies, superior weapons and experienced generals and soldiers. The whole of Kalinga was plundered and destroyed: Ashoka's later edicts say that about 100,000 people were killed on the Kalinga side and 10,000 from Ashoka's army; thousands of men and women were deported.
Embrace of Buddhism
The Ashoka Chakra, featured on the flag of the Republic of IndiaAs the legend goes, one day after the war was over Ashoka ventured out to roam the eastern city and all he could see were burnt houses and scattered corpses. This sight made him sick and he cried the famous quotation, "What have I done?" Upon his return to Paliputra, he could, acccording to legends, get no sleep and was constantly haunted by his deeds in Kalinga. The brutality of the conquest led him to adopt Buddhism and he used his position to propagate the relatively new philosophy to new heights, as far as ancient Rome and Egypt.
As legend goes, there was also another factor that lead Ashoka to Buddhism. A Mauryan princess who had been married to one of Ashoka's brothers (who Ashoka executed) fled her palace with a maid, fearing for her unborn child. After much travel, the pregnant princess collapsed under a tree in the forest, and the maid ran to a nearby ashram to fetch a priest or physician to help. Meanwhile, under the tree, the princess gave birth to a son. The young prince was brought up by the Brahmins of the ashram and educated by them. Later, when he was around thirteen years old, he caught the eye of Ashoka, who was surprised to see such a young boy dressed as a sage. When the boy calmly revealed who he was, it seemed that Ashoka was moved by guilt and compassion, and moved the boy and his mother into the palace.
Meanwhile Queen Devi, who was a Buddhist, had brought up her children in that faith, and apparently left Ashoka after she saw the horrors of Kalinga. Ashoka was grieved by this, and was counselled by his nephew (who had been raised in the ashram and was more priest than prince) to embrace his dharma and draw away from war. Prince Mahindra and Princess Sanghamitra, the children of Queen Devi, abhorred violence and bloodshed, but knew that as royals war would be a part of their lives. They therefore asked Ashoka for permission to join the Buddhist monks, which Ashoka reluctantly granted. The two siblings established Buddhism in Ceylon (now Sri Lanka).
From that point Ashoka, who had been described as "the cruel Ashoka" (Chandashoka), started to be described as "the pious Ashoka" (Dharmashoka). He propagated the Vibhajjvada school of Buddhism and preached it within his domain and worldwide from about 250 BC. Emperor Ashoka undoubtedly has to be credited with the first serious attempt to develop a Buddhist policy.
Silver punch-mark coins of the Mauryan empire, bear Buddhist symbols such as the Dharmacakra, the elephant (previous form of the Buddha), the tree under which enlightenment happened, and the burial mound where the Buddha died (obverse). 3rd century BC.
Policy
Emperor Ashoka built thousands of Stupas and Viharas for Buddhist followers (the Ashokavadana says 84,000 such monuments were built). The Stupas of Sanchi are world famous and the stupa named Sanchi Stupa 1 was built by Emperor Ashoka. During the remaining portion of Ashoka's reign, he pursued an official policy of nonviolence or ahimsa. Even the unnecessary slaughter or mutilation of animals was immediately abolished. Wildlife became protected by the king's law against sport hunting and branding. Limited hunting was permitted for consumption reasons but Ashoka also promoted the concept of vegetarianism. Enormous resthouses were built through the empire to house travellers and pilgrims free of charge. Ashoka also showed mercy to those imprisoned, allowing them outside one day each year. He attempted to raise the professional ambition of the common man by building universities for study and water transit and irrigation systems for trade and agriculture. He treated his subjects as equals regardless of their religion, politics and caste. The weaker kingdoms surrounding his, which could so easily be overthrown, were instead made to be well-respected allies. In all these respects, Ashoka far exceeded even modern-day world leaders.
He is acclaimed for constructing hospitals for animals and people alike, and renovating major roads throughout India. Dharmashoka defined the main principles of dharma (dhamma in Pâli) as nonviolence, tolerance of all sects and opinions, obedience to parents, respect for the Brahmins and other religious teachers and priests, liberal towards friends, humane treatment of servants, and generosity towards all. These principles suggest a general ethic of behavior to which no religious or social group could object.
The Edicts of Ashoka
The Ashoka Pillar at Sarnath is the most popular of the relics left by Ashoka. Made of sandstone, this pillar records the visit of the emperor to Sarnath, in the 3rd century BC. It has a four-lion capital (four lions standing back to back) which was adopted as the emblem of the modern Indian republic. The lion symbolises both Ashoka's imperial rule and the kingship of the Buddha. In translating these monuments, historians learn the bulk of what is assumed to have been true fact of the Maurya Empire. It is difficult to determine whether certain events ever happened, but the stone etchings depict clearly of how Ashoka wanted to be thought and how he wanted to be remembered.
Ashoka's own words as known from his Edicts are: "All men are my children. I am like a father to them. As every father desires the good and the happiness of his children, I wish that all men should be happy always." Edward D'Cruz interprets the Ashokan dharma as a "religion to be used as a symbol of a new imperial unity and a cementing force to weld the diverse and heterogeneous elements of the empire".
Missions to spread the Dharma
Asoka was the sponsor of the third buddhist council of Vibhajjavada (current Theravada) buddhism. After this council he sent buddhist monks to spread this religion to other countries, which were known to him at the time. The following table is a list of the countries he sent missionaries to, as described in the Mahavamsa, XII [3]:
Country name Name of leader of mission
(1) Kashmir-Gandhara Majjhantika
(2) Mahisamandala (Mysore) Mahadeva
(3) Vanavasi Rakkhita
(4) Aparantaka (Gujarat and Sindh) the Yona Dhammarakkhita
(5) Maharattha Mahadhammarakkhita
(6) "Country of the Yona" (Bactria/ Seleucid Empire) Maharakkhita
(7) Himavanta (Nepal) Majjhima
(8) Suvannabhumi (Thailand/ Myanmar) Sona and Uttara
(9) Lankadipa (Sri Lanka) Mahamahinda (Asoka's son)
Regarding the "Country of the Yona", Ashoka further specifies in his Edict No 13 (quoted hereafter), that most Hellenistic rulers of the period (Antiochus II Theos, Ptolemy II Philadelphus, Antigonus Gonatas, Magas of Cyrene and Alexander II of Epirus) received the teaching of the "Dharma". In the same Edict, Ashoka also adds the Cholas and the Pandyas as recipient of the faith.
Relations with the Hellenistic world
Lots more info and pictures at:
http://en.wikipedia.org/wiki/Ashoka#Embrace_of_Buddhism