Wikipedia
Shakubuku is a term that originates in the Chinese Śrīmālādevī Siṃhanāda Sūtra. Although often associated with the teachings of Nichiren, the term appears often in the SAT Daizokyo and the works of the Chinese Tiantai patriarachs Zhiyi and Zhanran.
It often refers to the proselytization and conversion of new adherents in Nichiren Buddhism (see second President of Soka Gakkai Josei Toda). Shakubuku refers to the rebuttal of teachings regarded as heretical or preliminary.
Nichiren organisations like Kokuchūkai, Nichiren Shōshū and Soka Gakkai took the phrase "break and subdue" literally in the past. Even though the term as such is still being used within most of the groups mentioned, it is now used to underline or rather convince the counterpart of one's own interpretation of Buddhism.
Another form of propagation mentioned by Nichiren is , which underlines the individual's own insight on Buddhism. Nichiren himself referred to both methods in his . A combination of the two is known as .
The term shakubuku is used when proselytising adherents of other Buddhist traditions, while shōju is used when proselytising non-Buddhists. In effect, though, shakubuku and shōju refer to the same method of proselytization in the West today.