Most of the previous posts give pretty good examples from history of so-called "subordinate group status" causes. If you want to talk about more modern causes however, I think you have to consider that currently, subordination is ultimately a choice. When I think of a group as "subordinate" I first think of the work place. Workers are subordinate to their bosses. They choose to accept such terms when they agree to be hired.
Students should be subordinate to teachers (and school administrators), but in our current system, this is one category of subordination that is fought every day, either by apathy, student rebellion, or parents who fight for more student power in a given classroom situation.
I don't honestly see any clear cut situations that lead to subordinate group status in our current society, outside of personal choice to be subordinate, or not.