American slavery was a part of capitalism, sure. So were these other systems of forced and coerced labor. In the aftermath of the abolition of slavery, former slaveowners all across the globe sought to maintain their wealth and the profitability of their plantations and factories by (often violent) coercion and force. This involved laborers who were displaced and disconnected from family and support systems and had little alternative but to work under extremely harsh conditions, with wages withheld or so low that laborers were barely subsisting and never building toward a better future. As one example, when the Dutch abolished slavery (one of the very last countries to do so) in Suriname, they brought in people from India with the promise of well-compensated work to replace the slaves of African origin. Those Indians were then stuck in South America with no way of returning home and no support system -- instead of being well-compensated, they were effectively forced to labor for very low or withheld wages, under threat of force, with their only alternative being starvation. Several times, Dutch forces violently struck down any resistance to these conditions. That's what I'm talking about.
