The greatest change for the better in the Third World (from an admittedly amateur but deep and long-standing investigation) is in assigning Property Rights. It would create overnight trillions of dollars of value and an incipient middle class and rooted citizens.
Hernando de Soto on Property Rights & Rule of Law
https://www.povertycure.org/learn/media/hernando-de-soto-property-rights-rule-law