Complex sentence: In 1923, the ILGWU president Benjamin Schlesinger resigned and the convention elected Morris Sigman, who had served as the Secretay Treasurer of the ILGWU before resigning after a dispute with Schlesinger.
Split into simpler sentences: In 1923, the ILGWU president Benjamin Schlesinger resigned and the convention elected Morris Sigman, who had served as the Secretay Treasurer of the ILGWU. Sigman had served as Secretary Treasurer before resigning after a dispute with Schlesinger.