Buddhism is a philosophy based on the teachings of Lord Buddha (563 BCE-483 BCE), who was born as Siddhartha Gautama, a Shakya prince in Lumbini, Nepal. The teachings preached by Lord Buddha subsequently turned into a religion, known as Buddhism.
The core of Buddhism lies in the purification of mind and soul by realizing the truth and getting rid of the worldly desires. Basically, it was the principles of Karma in the doctrine of Buddhism that made the religion one of the major ones in the world.

Buddhism After The Buddha - The role of Ashoka
It was after the Buddha's death that the school of Buddhism spread slowly in India and then subsequently, throughout the world. However, it was at the time of the Indian emperor Ashoka that Buddhism took a pace to reach its height. After the tragic Kalinga war, Ashoka decided to follow the path of non-violence or 'ahimsa' and converted to Buddhism. He promoted the doctrines of Buddhism not only in his empire as Dhamma but in other regions as well. It was his promotional campaign that led to the construction of the Buddhist religious monasteries and stupas, which further facilitated the spread of Buddhism in countries like Sri Lanka, Tibet, China and Japan.

The Buddhist Councils And The Rise Of The Buddhist Sects

First Buddhist Council : It was merely three months after the death of the Buddha that the first Buddhist Council was held in Rajgriha (Modern Rajgir, India) under the guidance of a senior monk, Maha Kassapa. Almost all the Buddhist monks who had attained the 'arahantship' participated in the council, in which they unanimously agreed that no disciplinary rule regulated by Lord Buddha should be changed, and neither new rules should be introduced! Since there was no conflict among the monks regarding the doctrines of Buddhism, therefore, all the principles were divided into several parts, which were individually assigned to the senior monks and their disciples.
The main purpose of this division was only to ensure that no omissions and additions could be made to the original principles.

The Second Buddhist Council And The Formation Of Sthaviravadin and Mahasanghika Schools : One hundred years after the first Buddhist council, the second Buddhist council was held in Vaishali in 383 BCE to deal with the disputes related to the monastic discipline (Vinaya). The monks differed so severely in their opinions on the interpretations of the Buddha's teachings that a split was inevitable and further resulted in the formation of the Sthaviravadin (with orthodox view) and Mahasanghika (with liberal view) schools of Buddhism.

The Third Buddhist Council : The Indian emperor Ashoka convened the third Buddhist council at Patliputra (Now Patna, India) in 250 BCE. The council was held by the monk, Moggaliputta Tissa and aimed at the purification of the Buddhist movement by reconciling different schools of Buddhism.
The third Buddhist council formalised the Pali canon, Tripitaka, better known as the traditional Buddhist text directly transmitted from the Buddha. The Pali canon comprised the monastic discipline(Vinaya Pitaka), the Budddhist doctrine(Sutra Pitaka) and a new philosophy (Abhidharma Pitaka).

As per the proceedings of the third Buddhist council, emissaries, including Ashoka's son, Mahindra, were sent to various countries such as Sri Lanka, Ceylon and the Greek kingdoms in the west in order to spread Buddhism.
After the third Buddhist council, the ideological conflict between the Sthaviravadins and the Mahasanghikas became so intense that they parted their ways forever and were named as Theravadins and Mahayanas respectively.

The Fourth Buddhist Council : The Fourth Buddhist Council was convened by the Kushana emperor, Kanishka around 100 CE in Kashmir or Jalandhar. The council was attended by both the sects- the Mahayanas and the Theravadins. The monks edited the old texts and the council approved a new set of edited scriptures for the propagation of the Buddhist ideologies.
The forth Buddhist council is usually associated with the formal rise of the Mahayana sect, though the Theravadins do not recognize the authenticity of this council and call it a 'Council of heretical monks'. However, it is a fact that it was only after the fourth Buddhist council that the Mahayana Buddhism flourished and spread to Central Asia, China, Korea and Japan, and the works of Nagarjuna, Asanga, Shantideva, Vasubandhu and Ashvaghosha acted as an add on to it.

The Fifth Buddhist Council : The fifth Buddhist council was held in Mandalay, Burma(Present Myanmar) in 1871 CE under the supervision of three Elders, the Venerable Mahathera Jagarabhivamsa, the Venerable Narindabhidhaja, and the Venerable Mahathera Sumangalasami. The council, which was held in the reign of king Mindon, aimed at reciting all the teachings of the Buddha, and to examine them minutely if any of them had been changed, dropped or altered.
The council, attended by 2400 monks lasted for five months and the entire text of the Pali canon was revised and inscribed on 729 marble slabs after its recitation had been completed and unanimously approved.

The Sixth Buddhist Council : The sixth Buddhist Council was convened in 1954-56 at Kaba Aye in Rangoon(Present Yangon) with a purpose to affirm and preserve the genuine Dhamma and Vinaya. Almost 2500 Theravadin monks, who hailed from India, Myanmar, Cambodia, Sri Lanka, Laos, Nepal, Thailand and Vietnam attended the council and took part in the traditional recitation and examination of the Buddhist scriptures and Tripaitaka.
The sixth Buddhist council is considered to be a landmark in the history of Buddhism as the version of Tripitaka, which was examined and reproduced in the modern press in the Burmese script, is still recognised as being true to the pristine teachings of the Lord Buddha.

Other Schools
It was due to the patronage provided by the rulers to Buddhism, that it was gaining popularity not only in India, but in the other places as well. The merchants, monks and pilgrims further took the wave of Buddhism as far as Arabia to the west and eastward to the Southeast Asia.
Mahayana Buddhism, which was spreading its root in other regions after the Indian subcontinent, established a major regional centre in Gandhar (Modern Afghanistan), from where it further spread to Japan, China, Korea and Mongolia. Bodhidharma, a Mahayana Buddhist, travelled to China from India in 475 CE and established the Chan school of Buddhism in China, which when further went to Japan, came to be known as Zen.
Another school of Buddhism, Tantaryana or Vajrayana developed in Eastern India (present Bengal and Orissa) and flourished during the period of Buddhism's decline in India from 8th to 13th century CE. This new school though was considered to be a sub sect of the Mahayana school, but believed in different way and practices. The Tantrayana Buddhism even today facilitates an accelerated path to enlightenment to be achieved through the use of tantra techniques, which are practical aids to spiritual development and esoteric transmission. The new thought first got spread in Tibet, Bhutan, southwest China and Mongolia by the Indian teachers, then later moved further towards Japan (Known as Shingon Buddhism) and Kalmykia, the only Buddhist state of Europe.

Buddhist Scriptures
The first disciple of Buddha, Ananda wrote down Buddha's thoughts and sermons (From first one at Banaras to the last one at Kushinagar) after His death. These texts, known as Tripitaka or the Three baskets became the main Buddhist scriptures.
Later the Mahayanas added the 'Lotus Sutra' and the 'Perfection of wisdom', 'Lankavatara' and many others to the Buddhist scriptures. Similarly, the Tantrayanas also compiled the holy scriptures of the 'Kanjur' (108 volumes), and the 'Tanjur' (225 volumes). Besides, the writings of the 6 Buddhist Councils are also considered as the Buddhist holy scriptures, which consists of 400 volumes.

Today, Buddhism is practiced widely in nations of the far east and few of the south Asian countries, whereas it has almost disappeared from India - the country of its origin. It was in the 7th-8th century CE that Buddhism began to decline in India, owing to the revival of Hinduism and Bhakti movement, and by the time of the Turkish invasion of India in 12th century CE, the wave of Buddhism had stayed calm due to the arrival of Islam in India. But, despite these challenges, Buddhism managed to sail through in other parts of the world, and still survives in some parts of India, its birthplace.