Tiananmen

15 years ago, the Chinese government, or then-Premier Li Peng ordered that military force will break up protest by mostly student that only wanted Democracy. To this day the Chinese government says that it only reacted. The exact number of the people that dies is to this day still unknown and attempts to bring up this subject within China have repeatedly been shut down.
The link above is to a search on google's news site.

I have been to Tiananmen square and to imagine this place being full of people protesting and then the military to move in is just breathtaking.