Complex sentence: On March 30,1972, two North Vietnamese Army divisions smashed through the Demilitarized Zone, marking the commencement of the Nguyen Hue Offensive, and they quickly overwhelmed South Vietnamese units in I Corps Tactical Zone.
Split into simpler sentences: On March 30,1972, two North Vietnamese Army divisions smashed through the Demilitarized Zone, marking the commencement of the Nguyen Hue Offensive. They quickly overwhelmed South Vietnamese units in the I Corps Tactical Zone.