Complex sentence: On May 21,1877, Johnson and his partners sold their company to the Western Development Company, a holding company for the partners who owned the Southern Pacific railroad, it was held as a subsidiary under its own name.
Split into simpler sentences: On May 21,1877, Johnson and his partners sold their company to the Western Development Company, a holding company for the partners who owned the Southern Pacific railroad. It was held as a subsidiary under its own name.