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A Japanese term for student activism that is often used for the New Left group from the 1960s to 70s and their political movements.
Various individual groups, political movements and incidents are associated with this term. For example the Zenkyoutou, Kakumaru-ha, Toudai Funsou, etc.
When one of those organizations, the Rengou Sekigun, caused the Asama-Sansou incident, they lost all support from the public and went into decline.
They are stereotyped as being equipped with construction helmets, dust masks and square timber (sometimes steel pipes and Molotov cocktails), sticking flyers with various propaganda slogans (for example, "Never allow!!" "Crush the unfair **!!" "We will win this conflict!!" etc.) all over the place, and for separating into numerous groups and infighting.
The various portmanteaus using Geba and Aji were created from student activism, and each derive from "gewalt" (German for "violence") and "agitation".
The square timber mentioned earlier are called geba-bou (gewalt stick), internal conflict is called uchi-geba (internal gewalt), flyers are aji-bira (agitation flyers), and the fonts used for these purposes are called geba-moji (gewalt fonts).