Complex sentence: People's Republic of Bangladesh was formed in 1971; where he was promoted to the rank of Lieutenant General and appointed-Chief of Army Staff of the Bangladesh Army in September 1986 subsequently by the then President Hossain Mohammad Ershad.
Split into simpler sentences: People's Republic of Bangladesh was formed in 1971; where he joined. He was promoted to the rank of Lieutenant General and appointed-Chief of Army Staff of the Bangladesh Army in September 1986 subsequently by the then President Hossain Mohammad Ershad.