First of all - which tyrants did the US overthrow? I presume you mean the British? I would strongly recommend doing some historical research instead of regurgitating what is essentially propaganda you've been fed all your life. Next you'll be telling us that the rebels were standing up against taxation that the British wanted to impose
I'm quite sure I mentioned something about matters of the 20th Century. Little hint there...
As for later oppressive governments - many, many people from different countries fought to end the threat of Nazism, not just the US and many of those were fighting while the US wasn't. For some countries WWII started in 1939 (or earlier).
Of course many countries fought against Nazism, that's not the point. The point is that without US involvement in those efforts arguably it's highly unlikely that Germany would have been defeated as it was, not to mention Japan's then aggressive imperialism. If true that US involvement made the difference in outcomes then the US culture leading to that involvement was an essential element leading to defeat of tyrants of the 20th Century. Gun ownership is part of that culture. As said already, whether that citizenry's culture would have developed as it did to perform as it did in the 20th Century without its precursors holding very personal views about gun ownership I don't know.
Besides, even if correct, to use that as some justification for justifying kids and teachers to be armed in order to avoid being gunned down today is simply a huge stretch IMO.
Who's argued that?