Complex sentence: Determining the O/B for VC and PAVN forces was complicated by the range of personnel involved, e.g., regular trained and equipped soldiers, different types of support (often called the Viet Cong Infrastructure), part time militias and guerrillas.
Split into simpler sentences: Determining the O/B for VC and PAVN forces was complicated because of the range of personnel involved. There were the trained and equipped'regular soldiers', different types of organized support (often called the Viet Cong Infrastructure), plus other groups, part time militias and guerrillas.