One modern form of slavery that exists does so via indentured servitude. If you owe any entity money, you are an indentured servant. Period. You are beholden to them. Owe on your house? You are a slave to the mortgage holder. Do you owe on your car? Slave. Do you owe on credit cards? Slave. You are under their control. You better make your payments, or they punish you.
Do you live paycheck to paycheck? Well, you are another type of slave. You are a slave to your boss. You must pacify them so that you don't piss them off and get fired. You are not free to be you, you are only free enough to be what they want.
The road to freedom is simply the removal of external control. Does freedom equal happiness? Not for everybody. Most people want some form of control. We don't, so our lives are focused hard on removing control where we can. We accept that being part of society implies complete freedom isn't possible, but there are a whole categories of freedoms many people freely give up that they don't have to.
Are you a slave?