Black January

Black January (), also known as Black Saturday or the January Massacre, was a massacre by the Soviet Red Army and the KGB secret police agency of peaceful Azerbaijani protesters of the Azerbaijani independence movement. It happened in Baku, Azerbaijan Soviet Socialist Republic on 19–20 January 1990, during the last years of the Soviet Union. Between 133-137 people were killed, when the Red Army and the KGB shot the protesters. As a result, the Azerbaijanis became totally opposed to stay a part of the Soviet Union and started to plan the independence of Azerbaijan. This happened with the end of the Soviet Union in December 1991.
It was one of the rare events during the liberal reform era of "glasnost" (reform of the government) and "perestroika" (reform of the economy) in which the Soviet Union used force against peaceful protesters. Before this era, the Soviet Union did not allow any protests of its population and stopped them violently if they did protest. 
The reason for using violence, was that powerful conservative people in the Communist Party, the Red Army and the KGB did not like these reforms and feared that the ethnic groups and republics of the Soviet Union were getting out of their control with the rise of nationalism. 
However, the use of violence angered the people in Azerbaijan and the rest of the Soviet Union. It had the opposite effect, because the liberal Soviet leaders and their reforms were too popular and powerful in the end. Neither the use of force against protesters nor the reforms prevented the republics becoming independent.