The United Nations Refugee Agency reports that one person is forcibly displaced from their home every two seconds as a result of conflict or persecution. We have seen the photographs of Syrian refugee camps in Turkey and Lebanon, and read about Somali refugees flooding into Yemen. Worldwide, refugees—citizens who flee their own country for another—number more than 20 million. But that number is dwarfed by a more silent and devastating crisis: the over 40 million who are internally displaced.