So the meaning of this sentence is that China's absolute monarchy was completely abolished through the propaganda of democratic ideas in the New Culture Movement.
One of the backgrounds of the New Culture Movement at that time was that after the victory of the Revolution of 1911 was stolen by Yuan Shikai, Yuan Shikai vigorously publicized the feudal ideology and culture represented by Confucius and set off a countercurrent of "respecting Confucius and restoring the ancients" in an attempt to prepare for the restoration of the monarchy. It is against this background that the elites of the New Culture Movement put forward the slogans of "Mr. De" and "Mr. Sai" (Mr. Sai refers to science), and opposed feudal ideology and culture with western scientific and democratic ideas. Liberated the people's minds and gradually made the idea of absolute monarchy withdraw from the historical stage.
In other words, the slogan of "Mr. De" is democracy, which is the slogan of the bourgeoisie to promote democracy, oppose feudal autocracy and point the finger at Confucianism, the theoretical pillar of feudal autocracy. This slogan reflects the requirements of China's social development and the urgent needs of the people, and has effectively promoted the development of the New Culture Movement. It also creates a good opportunity for the wide spread of new ideas and theories.