The importance of the conventional Sangha of monks as the principal agent for expanding and perpetuating the Noble Sangha of disciples has been realized throughout the long history of Buddhism. Thus, a small Sangha of monks was dispatched to foreign lands or distant places to spread Buddhism. Often, only one monk or a group of two or three monks were sent out to do this task and the monk or the group had to depend on local men to believe and ordain before a local Sangha of monks could be established.
In the early periods, especially at the beginning of the career of the Buddha, the members of the Sangha of monks were also Ariya, or members of the Noble Sangha. Their mission, therefore, turned only outward to increase the membership in the Noble Sangha and to receive those who were willing and prepared into the monastic Sangha. As time went on and the monastic Sangha became greatly enlarged, the number of members of the monastic Sangha who were not yet entitled to the membership in the Noble Sangha increased. The monastic Sangha then functioned more and more as the centre for training the unenlightened members, and the energy of the leaders in the monastic Sangha had to be divided between the inside and the outside of the monasteries, sometimes too much on the inside, to the neglect of the mission for the benefit of the outside. However, generally speaking, once a monastic Sangha has been established in a land, Buddhism is established there.
The different monastic Sanghas in different lands and countries lived and worked in different surroundings and among peoples of different cultures. With the passing of time, throughout the centuries, they developed some new roles and traditions of their own which were local. Some of these roles and traditions developed even at the expense of the original fundamental function of perpetuating the Noble Sangha of disciples. In spite of all local differences, however, the Vinaya keeps the various local monastic Sanghas, although geographically far apart, not too dissimilar to one another.
It is impossible to treat here of all the monastic Sanghas in so many different countries. As the Thai Sangha of today is said to be the largest monastic community in the world, it will be dealt with here as an example.