Complex sentence: Manekshaw rose to become the 8th Chief of Army Staff in 1969, and under his command, Indian forces conducted victorious campaigns against Pakistan in the Indo-Pakistani War of 1971 that led to the creation of Bangladesh in December 1971.
Split into simpler sentences: Manekshaw rose to become the 8th Chief of Army Staff in 1969. Under his command, Indian forces conducted victorious campaigns against Pakistan in the Indo-Pakistani War of 1971 that led to the creation of Bangladesh in December 1971.