Complex sentence: The U.S. diplomatic presence in Saigon was originally in the form of a consulate that was established on December 9,1907 as a representative to French Indochina succeeding an American commercial agent established in Saigon in 1889.
Split into simpler sentences: The U.S. diplomatic presence in Saigon was established on December 9,1907 as a consulate. It acted as a representative to French Indochina succeeding an American commercial agent that had been established in Saigon in 1889.