Complex sentence: He has written 30 books, mostly on the history and philosophy of Chabad Hasidism but also including biographies of the founder of modern Hasidism the Baal Shem Tov and the second generational leader of Hasidism Dov Ber of Mezeritch.
Split into simpler sentences: He has written 30 books, mostly on the history and philosophy of Chabad Hasidism. Other topics included biographies of the founder of modern Hasidism the Baal Shem Tov and the second generational leader of Hasidism Dov Ber of Mezeritch.