A government that is outwardly democratic (representative or participatory) can restrict voting rights to a particular group of citizens.
It isn't that. The group ignored isn't even considered in most cases. There have been several waves of suffrage since the greek days.
The general arguement used is that the uncounted group (Women, working class men, various racial distinctions) were weakminded, or if not that under the control of an already existing class.
Citizens in ancient greece had to be land-owners (and male and greek and head of the household of course).
This meant that if you weren't a land owner it was thought that you would vote as your landlord. What would be the point of granting tennants suffrage, that would just balance the vote towards those with many tennants.
Then married men would get an extra vote, at the time of female suffrage.
It wasn't a deliberate repression, just a complete failure to exist in the worldview.
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Slavery is a fuzzy term. If someone controls your life and death, and can treat you like property to be used and discarded...
... then I really shouldn't live in a society that could ever call a draft.
I wouldn't call that slavery as such, as in some way it is enslavement of self (assuming those subject to the draft have suffrage).
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Pulling back to indentured servitude, even concepts such as "Company stores" have this in the modern day. Any situation where an excessive salary is offered, but prefaced by a loan being taken out, should set off warning signs, being a trademark of people trafficking and the above situation.
Sixteen Tons is an interesting illustration of this.
I suspect capitalism (which isn't a government type - see the above comment about democracies) encourages indentured servitude. Any situation to the economic advantage of one party over another using any legal (or hard to catch) method is encouraged.
In some ways the classic "merchant" traveller game could be considered indentured servitude in a twisted kind of way.
Consider the PC's, each with a share in a very expensive ship that they owe an enourmous amount of money for. They need to continuously do dodgy high risk ventures to stay ahead of their loan, and to keep up with the repairs and maintenance on their vessel. Else it wouldn't be any fun.
The holders of the loan get benefit from holding the loan - return on investment - in a non-inflationary universe, without any risk to themselves. The lure of enourmous profits has been dangled in front of the PC's, followed by crippling repayments and expensive refits, trapping them.
Hmmmmmm.