This wikipedia article claims that "The Libyan population has increased rapidly after 1969. They were only 523,176 humans in 1911, 2 million in 1968, and 5 million in 1969."
Is this true? How could Libya gain 3 million more people in just 1 year?
1969 seems like a typo(Perhaps they meant 1999?). The population increase was quite rapid, however.
According to Libya: A Country Study from the Library of Congress, the population was 1.54 million in 1964, 2.29 million in 1973, reaching 3.6 million in 1984.
Policy that encouraged large families, oil wealth that allowed for increased healthcare spending, and foreign workers migrating to Libya seemed to be some of the factors that caused the population increase.