Indians traveled to other countries in ancient times for trade and to spread Buddhism, but were never formed as diaspora. The migration in ancient India was sporadic. After British started trade with India, migration of Indians happened in a large scale to other British colonies. Migration in India during colonial period is basically of two types - "indentured labour system" and the "kangani" system.
When Britishers arrived here, India was politically fragmented and its economy is in shambles. Science and technology was ceased developing. Earlier, there was rich talent in India in all fields that include engineering, agriculture, architecture etc. But the scenario is quite different when Britishers came to India as traders. They deteriorated the situation by assigning responsibilities of rent collection on landlords. This worsened the situation of agriculture. Farmers couldn't meet their ends. Britishers took advantage of this situation and exploited the poor by sending them to their other colonies as indenture laborers.
A lot of factors led to the evolution of indenture labour system. British administration needed labour to work on cane production, which was termed as 'industrial agriculture'. The demand for sugar was rising at that time. The indigenous population in colonies were too weak and traumatized to work in the fields. In 1834, slavery was officially terminated due to the demand of social activists in European countries. Then, private firms and British administration together started indenture labour system and started exploiting the innocence of poor in India. They sent several people to Mauritius, West Indies, Fiji, Jamaica and many other colonies. All of them were lured into this by false promises and assurance of better life. They were promised that this is an agreement of just five years and after that they will gain rights as citizens in their new homeland. But the promises were never kept, and the migrants status was further worsened in the new places.
Sever people that were taken as indentured laborers were abused and killed in the transportation through waterways. After a few years, common people came to know about abuse of laborers and a committee is formed as a probe. It lead to banning of migration to several colonies and thereafter the ban was diluted.
Emigration to Burma, Srilanka and Malaya is different to emigration to Mauritius and West Indies. In these countries, migrants used to be recruited by 'Kangani', the headmen who is a migrant himself. Situations here were different. Though the demand of laborers decreased with time, unrecruited and free migration took place to these countries. Other than this, several educated Indians migrated to developed countries for better life.
Indians who are migrated to different countries for different reasons, formed communities at their places and settled in their new homelands. Many of them are still attached to Indian culture and communities, while several others assimilated into the culture of their new homelands. For example, Indians settled in Thailand took Thai names and completely mingled with people there. Though migration of Indians is happening continuously, massive migration happened during colonial rule.