Slavery and Kant's Doctrine of Right

In the 1780s through the end of 1790s, Kant made various references to slavery (in its different forms) and the transatlantic slave trade in the context of his political philosophy or philosophy of right; he thereby had opportunities to speak in favor of abolitionism, which was gaining momentum in parts of Europe, or at least to articulate a normative critique of the race-based chattel slavery or Atlantic slavery and the associated slave trade qua (legalized) INSTITUTIONS; but he did neither. Why? In raising and seeking an answer to this question, I am not interested in what Kant’s normative silence about the institutions of Atlantic slavery and slave trade may tell us about him as a person (for example, whether he was blinded by his own racist prejudices or whether he was affected by some kind of cognitive dissonance). Rather, I will focus on what it may tell us about certain limitations of his political philosophy, limitations that might have made it THEORETICALLY DIFFICULT for him to figure out exactly what to DO about those institutions as entrenched political realities.