I also don't think you see the end of slavery *without* capitalism, either, because it's the riches of industry that enabled powerful states to wean themselves off of revenues from slave plantations (and even start violently suppressing the vile practice). Liberalism gave the ends but not the means

It really matters that the Northern US was overwhelmingly economically superior to the South, and it was overwhelmingly economically superior because it fully embraced industrialism and capitalism while Southern planters hobbled both of them locally by artificially driving down the value of labor.