A country’s diaspora can be a symbol of its pride and power. A nation’s diaspora can help it build international value through success stories, promote its soft power through culture and contribute to its economic progress through remittances, investments and transfers of expertise. India and China have among the world’s largest diasporas. They also offer two very different models of how countries can leverage their diasporas. In India, before the 1991 reforms, people mostly saw those who left...