"End of the movement
"By February 1967 political opinion at the center had decided on the removal of the Red Guards from the Cultural Revolution scene in the interest of stability. The People's Liberation Army (PLA) forcibly suppressed the more radical Red Guard groups in Sichuan, Anhui, Hunan, Fujian, and Hubei provinces in February and March. Students were ordered to return to schools; student radicalism was branded 'counterrevolutionary' and banned. There was a wide backlash in the spring against the suppression, with student attacks on any symbol of authority and PLA units. An order from Mao, the Cultural Revolution Group, the State Council, and the Central Military Affairs Committee of the PLA on 5 September 1967 instructed the PLA to restore order to China.
"The PLA violently put down the national Red Guard movement in the year that followed, with the suppression often brutal. A radical alliance of Red Guard groups in Hunan province called the Sheng Wu Lien was involved in clashes with local PLA units, for example, and in the first half of 1968 was forcibly suppressed. At the same time the PLA carried out mass executions of Red Guards in Guangxi province that were unprecedented in the Cultural Revolution. The final remnants of the movement were defeated in Peking in the summer of 1968. Reportedly, in an audience of the Red Guard leaders with Mao, the Chairman informed them gently of the end of the movement with a tear in his eye. The repression of the students by the PLA was not as gentle. After the summer of 1968 some more-radical students continued to travel across China and play an unofficial part in the Cultural Revolution, but by then the movement's official and substantial role was over."
https://en.wikipedia.org/wiki/Red_Guards_%28China%29#End_of_the_movement
You must not remember the campus Red Guards of the 60s. They are all professors now and have trained the New Red Guards such as have made their appearance at the U of Mo..