Answer:
Diaspora is migration during the era of nationalism, not just a scattering of peoples but also a politico-emotional gathering in far-off lands under the sign of the nation. Diaspora is an idea that only makes sense in the era of nationalism. Prior to nationalism’s birth in the 19th century, people moved routinely. They traveled from their local places of birth and social sustenance to territories so far that they lost touch with their early homes. Most of these migrants did not think of themselves as part of a coherent diaspora, mainly because they did not see their places of origin as part of a national project. When people of the Indian subcontinent (desis, or those from the desh, homeland), for instance, commonly traveled to Southeast Asia or to Africa as part of the world of the Indian Ocean (that has been called the Afrasian Sea), there is no evidence that they saw themselves as part of a desi diaspora. [note 1] On the contrary, they took with them social practices, habits and materials from their homelands, moved to far-off locales and set to work in the construction of a new ethos, one that was defined in conversation with the materials and ideas that they found in those parts.
The ancient and early modern migrations of people from the Indian subcontinent are a prelude to the diaspora of the 19th century and after, but they are not a part of it. What defines the diaspora of the 19th century onwards, in the era of nationalism, is that as people left a homeland that was already seen as a “nation,” they continued to bear fond memories of that homeland and saw themselves as somewhat patriotic to it. Even though the word diaspora comes to us from the Greek for scattering (which implies any migration) and even though it is classically used to refer to the Jewish Diaspora after the destruction of the Temple in 70 C.E. [note 2], the concept in modern times refers specifically to the idea of a departure from a national homeland and a nostalgia for that homeland. Thus the two kinds of migration should not be conflated.
Explanation: