One of the assumed truths in the US is that an armed citizenry will prevent the US government from becoming oppressive and taking away our liberties.  Recently I have seen people state that the Tea Party folks brought guns to their rallies and the police were respectful of their rights to assemble, but the Occupy movement (and various left-oriented movements in the past) didn't have guns and so got attacked by the police.

I am curious about this line of reasoning and have been seeking an actual instance of when an armed citizenry prevented government oppression. 

I can think of examples where an armed citizenry didn't stop government oppression such as:

• Shay's Rebellion,
• the Whisky Rebellion,
• post-civil war oppression and disenfranchisement of African-Americans,
• the anarchists around the turn of last century and
• the internment of the Japanese during World War II,
• the treatment of the Black Panther Party in the 60/70s. 

Indeed that the anarchists or Black Panther party had weapons (and sometimes used them in self-defense) were used as excuses to use overwhelming government power and surveillance on them, which is part of the reason nonviolent tactics proved more effective. 

Are there instances where firearms really did stop government oppression or did they only serve to bolster the power and privileges of the (generally) white wealthy power structure?  I know some of you will think the question is loaded, but I am seriously trying to find an instance where firearms did stop government oppression.