Antananarivo has been the largest city on the island since at least the late 18th century, when its population was estimated at 15,000. By 1810, the population had grown to 80,000 before declining dramatically between 1829 and 1842 during the reigns of Radama I and especially Ranavalona I. Because of a combination of war, forced labor, disease and harsh measures of justice, the population of Imerina fell from 750,000 to 130,000 during this period. In the final years of the Kingdom of Imerina, the population had recovered to between 50,000 and 75,000; most of the population were slaves who were largely captured in provincial military campaigns. In 1950, Antananarivos population was around 175,000. By the late 1990s the population of the metropolitan area had reached 1.4 million, and – while the city itself now has a population (2013) of about 1,300,000 – with suburbs lying outside the city limits it had grown to almost 2.1 million in 2013. The metropolitan area is thus home to 10 percent of the islands residents. Rural migration to the capital propels this growth; the citys population exceeds that of the other five provincial capitals combined.
Question: How many causes were there for the population decline from 1829 to 1842?
Answer: 4