In the Civil War in Finland, 1918, the Red Guards were the supporters of revolution who were defeated by the White Guards and German forces.
Red Guards is, with regard to the Russia and the Soviet Union, just another English name for the Red Army.
During the Civil War in Russia, 1918-1920, the Red Guards defeated the White guards, or simply the Whites, who together with West-European intervening forces supported the monarchists, democrats and conservatives who opposed the Russian Bolshevist October Revolution supported by the Red Guards.
In the People's Republic of China, the Red Guards (紅衛兵) were civilians who were the frontline implementers of the Chinese Cultural Revolution (1960s-1970s). Most Red Guards were youngsters in their mid-teens summoned by Chairman Mao Zedong to protect the forward progression of the Chinese Socialist Movement against "evil forces" such as imperialism and corruption. They used the occasion to re-educate those who committed crimes against the People such as the bourgeois and corrupt leaders of the Communist Party of China.
[Caution: The content below may not be NPOV.]
Many young Chinese were enthusiastic about the prospect of "being politically influential at such young age". With Little Red Books in their hands, squads of Red Guards formed and began to go from house to house looking for potential elements of corruption which sometimes included teachers, relatives, and then their own families. The accusation against their victims were becoming more and more ridiculous as well. Someone might be punished for not owning an "extra set" of the Chairman's publications. The punishment could be exceptionally cruel. Some victims were forced to chew on shattered glass, while others would be forced to strip naked and march through town. The situation quickly turned out to be downright ugly. The number of people who perished during the period was estimated to be in the millions.
There were cases where particular members would start by going after their parents in order to display uncompromising fairness and absolute obedience to Mao. Then others would have to measure up or even surpass these efforts, and whole thing would fall into a vicious cycle.
Following Mao's death and the Gang of Four's demise in 1976, the Cultural Revolution officially ended. During the late-1970s and early-1980s, numerous ex-Red Guards who were identified as having committed serious crimes against humanity during the revolution were finally tried and sentenced to prison, some were even executed. However, the physical and psychological scars they inflicted on their victims may never heal. Those ex-Red Guards who escaped punishment are not rejoicing either, as most have missed their chance for education; they are now left helplessly at the bottom of the food-chain despite mainland China's booming economy. In retrospect, the ex-Red Guards who were celebrated so early in their lives, are now collectively referred to as the Lost Generation.