The Vietnam War was a counterinsurgency that involved us in guerrilla

Please respond to the following Question: 

The Vietnam War was a counterinsurgency that involved us in guerrilla warfare that was similar, in some ways, to what we face in Afghanistan today. But the way the Vietnam War was conducted was considered to be immoral and unjust by many.

Describe the prevailing arguments of what constitutes a "just war," and assess the justice of the Vietnam War in that context.

Speculate on how the world would be different today if the U.S. had not become involved in Vietnam.