Complex sentence: He left the army because of professional conflicts with Shah Mohammad Reza Pahlavi and retired in 1973, after resignation from army he became Iranian ambassador in Spain for few years up to 1978.
Split into simpler sentences: He left the army because of professional conflicts with Shah Mohammad Reza Pahlavi and retired in 1973. After resignation from the army he became Iranian ambassador in Spain for a few years up to 1978.