IF YOUR surname is McNamara and you live outside Ireland, expect a letter. Ireland Reaching Out, a non-profit organisation financed largely by the Irish government, has pioneered what it calls “reverse genealogy”. Rather than waiting for people to trace their Irish ancestry, it constructs family trees from root to branch, tracking down the descendants of those who left for America, Australia and other countries. Volunteers then invite them to visit the homeland. It is a mighty task: Mike Feerick, the outfit’s founder, wants to build a database of the Irish diaspora containing 30m or 40m names.

Last year Ireland appointed its first minister for the Irish diaspora; this spring it unveiled a diaspora strategy. As well as Ireland Reaching Out, the government supports hundreds of groups that serve needy Irish emigrants or court successful ones. One of them, Connect Ireland, uses the diaspora as spies for inward investment: it pays for tip-offs that lead to foreign companies creating jobs in the country.

In the early 1980s barely a dozen countries had a ministry, a government department or some other official institution dedicated to their diasporas. And a few countries, including America, still ignore those who have left—except perhaps to send them tax demands. But these are a shrinking minority (see chart). Kingsley Aikins, an Irishman who advises governments on how to deal with their far-flung folk, has travelled in the past few weeks to Lebanon, Malawi and Wales.

Ministers and bureaucrats are multiplying partly because diasporas are too. The World Bank reckons that about 250m people live outside the country of their birth; the number of foreign migrants living in OECD countries rose by 38% in the 2000s. And diasporas are not just composed of emigrants. The Irish government thinks that everybody of Irish descent—perhaps 60m or 70m people—is part of the Irish diaspora. Israel claims all Jews. Countries are also paying more attention these days because they believe their diasporas can make them rich. When the World Bank began to publish estimates of remittance flows in 2003, “you could see the dollar signs flashing in finance ministers’ eyes,” says Kathleen Newland of the Migration Policy Institute, a think-tank. And that was only the beginning of an infatuation. Politicians and officials have since concluded that diasporas can help cure an extraordinarily wide range of national ills, from poor global reputations to weak infrastructure to a shortage of scientific talent. But can they? A few months after his victory in India’s elections last year, Narendra Modi addressed a whooping crowd of some 20,000 Indian-Americans in Madison Square Garden in New York. Thanks to them, the new prime minister said, India was no longer seen as a land of snake charmers but as a technology powerhouse. This was flattery, but with serious intent. India sees its diaspora, which the government thinks is about 25m strong, as a means of projecting soft power and burnishing the country’s image. “No country has had such a large brain drain and been so proud of it,” says Devesh Kapur of the University of Pennsylvania. Inspired partly by the example of Israel, many countries have come to believe that their diasporas can advance their geopolitical interests. The Turkish government counts on its diaspora in Europe, especially Germany, to push for closer relations with the EU; Mexico knows that Mexican-Americans will campaign against attempts to crack down on illegal immigrants. In exchange for their help, and to bind them to the politics of their homeland, a growing number of countries offer diasporas long-term visas (as India has done), dual citizenship or some voting rights. In 2010 France’s parliament created 11 new constituencies for the French abroad.

Poor and middle-income countries also see their diasporas as a source of cash. Emigrants send remittances, often in vast quantities—India receives $70 billion a year, and remittances to Tajikistan are worth half of the country’s GDP. Because they are a source of foreign exchange, rating agencies can take remittances into account when assessing a country’s creditworthiness. Future flows of money can be securitised, as Brazil and Jamaica, among others, have done. Governments have also hawked infrastructure bonds to their diasporas, who might buy them for patriotic reasons, and also might not object to repayment in local currency. Israel, which has been doing this since 1951, is once again the country to copy.

Prodigious sons

These days, however, diasporas are increasingly seen as talent pools that can be pumped. When its economy crashed in 2009, Ireland summoned some of its most successful overseas progeny to an economic forum, which continues to meet every two years. Mexico used to think of its diaspora in America mostly as working-class remittance senders. It now encourages its young citizens to study in American universities—and then bring their skills home. Ghana, which has a particularly talented diaspora (see article), has set up a support unit to schmooze them.

No country is hungrier than China. Emulating Taiwan, which built a technology industry with the help of Taiwanese Stanford graduates, it is trying to woo its most talented foreign-educated citizens to come back; those who do are called “sea turtles”. Provincial cities offer tax breaks to returning entrepreneurs and create industrial parks for them. Under the “thousand talents” scheme (which is even more ambitious than it sounds) academics who have built careers abroad are offered far more money than is usually paid to Chinese professors. The wooing is broad and relentless: one Chinese-British academic contacted for this article had been approached that very morning.

She is not interested, though—and in that she is typical. Patrick Gaulé, a researcher in Prague, has tracked the careers of foreign-born scientists in America. He estimates that less than 9% will return during their working lives. Scientists from well-off countries are most likely to go back: the Taiwanese are about five times more likely to return than are the mainland Chinese, for example. Surveys of PhD students in America find that 82% of Chinese and 84% of Indians plan to stay.

Apart from all the obvious things that bind people to their adopted homes—friends, children in school, husbands and wives reluctant to leave—it is often hard to find jobs in the countries where they were born. Returnees may have fewer contacts than those who never left. And Kaifu Lee, who was born in Taiwan, worked in America and now invests in technology firms in China, says that although foreign-educated computer scientists are technically excellent, they can suffer from inflated expectations—the result, in part, of comparing themselves to the earlier returnees who built China’s great technology firms. And never mind the tax breaks and the industrial parks, he says: almost everybody who returns wants to be in big cities like Beijing, Shanghai and Shenzhen.

Nor can diasporas cure many financial ills. Whereas India and a few other countries have done well out of diaspora bonds, others (such as Ethiopia) have struggled to find buyers: expats turn out to be less patriotic and more hard-headed than is often supposed. Remittances are reliable—more so, in a recession, than foreign direct investment. But even these suffer from exchange-rate fluctuations: flows from Russia to Central Asia have plunged in dollar terms as the rouble has collapsed.

Trying to use diasporans to lobby for national interests is even harder. People leave countries for a reason, and that reason is often disdain. Mexicans “did not leave Mexico por gusto [for pleasure]”, says Carlos González Gutiérrez, the Mexican consul in Austin, Texas. Older migrants in particular frequently distrust the government. And expat politics is often a hothouse, in which intransigent views flourish and ancient battles are endlessly refought, whether or not they benefit the homeland.

Even when expats are on the side of the government, they are tough to wrangle. The American branch of Overseas Friends of BJP dispatched volunteers to India and manned phone banks during last year’s Indian elections. No sooner had its man, Mr Modi, been elected prime minister than the outfit sent him a list of demands. Overseas Indians would like the vote, please. They would also like more flights between America and India, kinder treatment at consulates, fewer restrictions on buying land and better arrangements for shipping dead bodies back to India.

A thankless, noble task

So the wooing is hard. Yet the effort is worthwhile, even if a country’s diaspora resists its entreaties. Indeed, it is worthwhile precisely because diasporas are so churlish and hard to court. The difficult things that expats tend to demand of their governments—representation, a good business climate, decent investment returns—are the sort of things that governments ought to be trying to provide anyway.

India reformed its antiquated venture-capital regulations at the instigation of Indian-Americans in Silicon Valley. China is now cutting some of the red tape that is required to start a business partly because of pressure from returnees, says Wang Huiyao of the Centre for China and Globalisation, a think-tank in Beijing. And China is no longer just trying to bring back its diaspora: it also wants Western talent.

“The diaspora is a powerful engine of change, and for good,” says Mr González Gutiérrez, in Texas. “They are the first people to advocate for openness, for free markets, for better-quality democracy.” Most countries could do with more of that.