In the American effort to rebuild Europe following World War II, it became clear to policy makers that private investment is a powerful generator of economic development and that there is an appropriate role for government in encouraging private investment where it has the potential to do the most good. Accordingly, the Marshall Plan authorized the U.S. government to insure private U.S. investors against the risk that earnings generated overseas in foreign currencies might not be convertible into U.S. dollars. This new tool—political risk insurance—was expanded in the 1950s to cover losses from war and expropriation, as well as government interference with investors' rights to the proceeds of their investments. It was subsequently complemented with the addition of project financing.