From “Modes of Production and Slavery in Madagascar: Two Case Studies” by Maurice Bloch, in Asian and African Systems of Slavery, ed. by James L. Watson (U. Calif. Press, 1980), pp. 103-105:
The connection of Madagascar on the one hand, and Mauritius and Reunion on the other, lay in in the fact that the East Coast of the great island was sometimes inhabited by small pirate colonies and sometimes by traders and adventurers who supplied the Mascarenes with rice and cattle but also, increasingly, with slaves to be used on the plantations of these islands (Filliot 1974:113-127). Up to 1770 the trading links between Madagascar, Mauritius and Reunion had been relatively small-scale and fluctuating over time. They had, however, been extremely significant in Madagascar in that they had supplied petty rulers with European weapons for their aggrandizement and slave raiding (Filliot 1974:205-208). Towards the end of the eighteenth century, however, the small but growing central state that was to become Imerina, profiting from the disarray of the Betsimisaraka League, captured most of this trade both canalising its network and reducing rivals. The trader Dumaine wrote in 1790 that Imerina ‘is the part of Madagascar which supplies most of the slaves for our islands’ (Mauritius and Reunion). This process was truly momentous in the history of Madagascar because in return for slaves the Merina obtained armaments of high quality in much greater quantities than had been available to anybody else before, since they were lucky in reaching the coast precisely at the time when the demand for slaves in the Mascarenes had boomed and the prices soared (Curtin 1969:266-269; Filliot 1974:62-65, 216).
The war materials that they obtained were probably the major cause of the continuing expansion of the Merina and their ultimate domination of the islands. This expansion, however, was itself in part necessitated by the need to supply slaves in ever greater numbers in order to obtain the armaments necessary for conquest (Bloch 1977:314). By engaging in this sort of trade in order to acquire political power the Merina were following a long tradition which had dominated the political process of Madagascar perhaps since as far back as the sixteenth century. We know this pattern well in the eighteenth century when the Sakalava and the Betsimisaraka managed to dominate large areas of the island by exporting slaves to various European or Arab traders in return for armaments which enabled them to conquer their neighbours and obtain more slaves. The process in the case of the Merina, however, was even more dramatic. The reason was that they captured the trade at a time when the Mascarene economies were booming and so was the demand for slaves.
Once the Merina kingdom had really become established through this process, the pattern began to change in a way which was particularly significant for the history of slavery. In 1814 Mauritius, as it was renamed, became British and, in taking over Mauritius, the British had also gained vague but promising rights over Madagascar. Farquhar, the Governor of Mauritius, therefore encouraged the trade between his island and Madagascar since he saw the expansion of a kingdom dependent on supplies from Britain as a first step towards conquest, a policy we are familiar with in other parts of Africa. This policy was not without difficulty as it was taking place at a time when public opinion in Britain was moving strongly against the slave trade and slavery. Farquhar at first resisted pressure for the abolition of the slave trade, arguing that, in the first place, it would ruin the economy of Mauritius and make his unruly subjects even more difficult to control and, in the second place, it would end the promising connection with the Merina which he intended to use for ultimate conquest.
By 1817, however, the pressure from Britain had so increased that he had to give way, although by then the two stumbling blocks to ending the slave trade with Madagascar had vanished. The economy of Mauritius had been moving away from its dependence on the importation of slaves. Secondly Farquhar had discovered a way whereby he could keep his Merina contact. He signed with Radama a treaty which in return for the abolition of the slave trade would guarantee Radama a yearly supply of armaments, as well as military assistance. By this treaty the British hoped to continue their influence in Madagascar and to ensure the ever-important supply of rice and cattle to Mauritius. This treaty had its ups and downs and for a significant period was abrogated altogether, but it remained the major template for British Merina relations during the nineteenth century. It also ensured that whenever it was in operation the Merina would be dependent on the British. For the Merina the advantage of this treaty is also obvious. Radama, the Merina King, still retained a steady supply of British armaments but gained as well, and this is probably the most significant point, a monopoly of European weapons in Madagascar, a monopoly which many tried to break but never with complete success. When the treaty was in operation British frigates patrolled Madagascar to stop any signs of the slave trade. In doing so they were stopping any potential rivals of Radama from obtaining arms with which to resist him. They were, so to speak, putting Madagascar in a vacuum in which only one group had access to modem weapons. Under such circumstances it is hardly surprising that nobody could offer any significant resistance to the Merina during their greatest period of expansion.