Complex sentence: The North Vietnamese built maintained, and expanded, under a deluge of bombs, over 3,000 kilometers of roads and paths through the mountains and jungles while only two percent of the troops sent south were killed by the American effort to halt their infiltration into South Vietnam.
Split into simpler sentences: The North Vietnamese built maintained, and expanded, under a deluge of bombs, over 3,000 kilometers of roads and paths through the mountains and jungles. Only two percent of the VPA troops sent south were killed by the American effort to halt their infiltration of South Vietnam.