“long term labor contracts, lacking many critical aspects of what in English is referred to as slavery (owners weren’t allowed to kill slaves, prohibition of sex with slaves, etc.).”
That isn’t completely true, as the length of service of an Eved Canaani was indefinite, and sex was at times permitted with them. But if they were freed they became full fledged Jews without kabalat hamitzvot, and they had to be educated in mitzvot and could not be abused. The comparison to the status of Africans in the US could not be more dramatic, as education was prohibited and abuse was routine .
Unfortunately, two of the leading orthodox rabbis in the US at the time of the Civil War did not understand this: Rabbi Bernard Illowy and Rabbi Morris Raphall. Fortunately there was one orthodox rabbi in the US who did: Rabbi Sabato Morais.
When William Seward, Lincoln’s Secretary of State, visited Eretz Yisrael after the war, the rabbis in Jerusalem made a blessing thanking HaShem for making the North victorious in the war, ending the anti-Biblical slavery. There is an article on the Aish HaTorah web site describing this.
May we eradicated the remaining slavery in the world and may it never return.