As the debate over immigration rages on, consider this: people who were born in one country, but then move somewhere else, have an estimated $400 billion in savings. These days, the old country sometimes comes back to the emigrants with an offer — lend us money.

Dan Lainer-Vos teaches sociology at the University of Southern California and has written a book about what are referred to as Diaspora bonds, and how they’re used by Irish and Israeli Americans, called “Sinews of the Nation.”