Why did the Betsimisaraka confederation decline after 1750?

The Betsimisaraka confederation, a quasi-state established along the eastern coast of Madagascar by Ratsimilaho, began an abrupt, prolonged disintegration following the death of its founder in 1750.12

While the confederation had successfully united various coastal chiefdoms during the early 18th century, it lacked the long-term structural stability to survive the loss of its central leadership. Following this decline, the region eventually fell under the influence of the expanding Merina kingdom, which sought to consolidate control over the island's coastal territories during the late 18th and early 19th centuries. The dynasty's rule ultimately collapsed entirely upon the death of its third ruler in 1791.123