Technological developments in the late 19th century such as the development of lithography and photography led to diversification and specialization among printers. Further fragmentation in the printing labor movement led to the establishment of the International Printing Pressmen Union of North America (IPPU), in 1889. In 1892, the ITU authorized membership for mailers and for newspaper writers. Pressure mounted for a separate pressman's union, and in 1892 the International Brotherhood of Bookbinders (IBB) was formed. Many pressmen left the ITU for the Bookbinders. At the same time as mailers joined, two thousand pressmen members seceded to form the International Printing Pressmen Union Assistants, (IPPUA) in 1897 and the International Stereotypers' and Electroplaters' Union, (IS&EU) in 1902. At the start of the 20th Century, ITU membership was primarily compositors and mailers.