Complex sentence: Ethel Jenner Rosenberg (August 6,1858-November 17,1930) became the first English Bahá'í when she converted in 1899, after having been introduced to the Bahá'í Faith by Mary Thornburgh-Cropper, an American resident in London who had converted in 1898.
Split into simpler sentences: Ethel Jenner Rosenberg (August 6,1858-November 17,1930) became the first English Bahá'í. Rosenberg became a Bahá'í when she converted in 1899, after having been introduced to the Bahá'í Faith by Mary Thornburgh-Cropper, an American resident in London who had converted in 1898.