He then resigned from this position to establish a yeshiva in the city, which eventually became world-famous first being led by the notable Naftoli Trop, followed by the esteemed son-in-law of his rabbi, Mendel Zaks.

He became one of the most influential rabbis within Orthodox Judaism during the late 19th and early 20th century, taking a central leadership role in the World Agudath Israel movement in Eastern Europe.

[8] Although the anti-religious attitudes which pervaded Zionism greatly distressed him, Kagan initially refused to become personally involved in the matter and refrained from publicly denouncing the movement.

[14] Elchonon Wasserman (killed in the Holocaust 6 July 1941) said that this means even if the majority of yeshivos would have to close, we would not be allowed to join the WZO.

In 1925, it was announced that he would be leaving Warsaw with his daughter and son-in-law to permanently settle in Petach Tikvah (the Gate of Hope, in Hebrew), in Palestine.

[15] Upon discovering his plans, prominent rabbis and yeshiva deans persuaded him to remain in Radin[16] and he died there on September 15, 1933, aged 95.

Orthodox Jews across the world viewed him as one of the 36 righteous people,[19] and Polish farmers were said to have lured him into their fields believing his feet would bring blessing to their crops.

[20] According to some reports, despite his rabbinic leadership he did not hold semikhah until late in life, when he had to apply for a passport and needed formal semichah in order to honestly enter "rabbi" as his occupation.