Note: I left some details out due to upcoming novels 

It would be fair to say that the Mithras treated the natives of the Caribbean in much the same way as Columbus and Spain did. They forced the natives to mine and then eventually cultivate sugar. Diseases killed over 80% of the native population. Like in our timeline, there was some loud outrage over the genocide, but the Mithrans do not turn to African slavery. Instead, as a political and economic response to the outcry, they performed inoculations(Europeans use this earlier in the timeline) and then legally put the natives under the yoke of Mithran slavery. Both solutions curtailed deaths, but official slavery did just as much to destroy the cultures of the natives and bind them to constant degradation.
The rape of these lands continues as does the enslavement of its native peoples. The area is also a haven for pirates and other criminals as Mithra, Tengra, the Nsundi Empire and the Palmyrene Empire(with Kymbri backing) fight over resources in the blue isles.
Mithra remains on top in this region and is the source of the nation's accumulated wealth which scare other nations not allied with them, hence using subterfuge to undermine each other so as not to start a full-scale war.

The Silent War
A war was waged between Mithra, Tengra, the Nsundi and the Palmyrene Empire. The Palmyrenes and Tengra did so on behalf of Kymbri. A treaty between the Mithra and Tengra was signed soon after, allowing Tengra a measure of control in the region as long as they rejected their Kymbrian backers. This left the Palmyrenes out to dry, creating a tense political situation in their wake.