I once saw Rav Hirsch make a passing reference to black slavery in America in his Collected Writings, but no longer remember where. Does anyone know where this might be?
The belief of our people in the Redeeming One inspired other oppressed people to have faith in eventual salvation. For example, Rabbi Hirsch mentions that this faith in eventual salvation gave “hope to the black slave in the plantation” (The Hirsch Haggadah, page 265). Rabbi Hirsch may have been aware that the slaves on plantations in the United States drew hope from the story of Israel’s liberation from bondage. In fact, one of their popular spirituals was “Go Down Moses” – a song based on the Passover story. The following is a stanza from this song: “Go down, Moses, way down in Egypt's land; Tell ol' Pharaoh, Let my people go!”
Excerpts from "Orthodox Approaches to Biblical Slavery" by Gamliel Shmalo - which appeared in The Torah u-Maddah Journal Volume 16 2012-2013
Rav S. R. Hirsch (Shemos 12:44): The consideration of certain circumstances is necessary, correctly to understand the fact that the Torah presupposes and allows the possession and purchase of slaves from abroad to a nation itself just released from slavery. No Jew could make any other human being into a slave. He could only acquire by purchase people who, by then universally accepted international law, were already slaves. But this transference into the property of a Jew was the one and only salvation for anybody who, according to the prevailing laws of the nations, was stamped as a slave. The terribly sad experiences of even the last century (Union, Jamaica 1865) teach us how completely unprotected and liable to the most inhuman treatment was the slave who in accordance with the national law was not emancipated, and even when emancipated, wherever he was, looked upon as still belonging to the slave class, or as a freed slave."