Four questions

1. Your community and nearly everyone you love have just been massacred. The surviving members of those who did it are getting away clean. Your whole way of life is gone. The American Dream is hollow. and so on and so on.

2. As Averill says, he's using the pretense of arresting the mercenaries to save them after it becomes clear that there not going to sweep through the town as planned. He's using the National Guards to save his own skin.

3. There the three only survivors. Why not finish the job?

4. Walken asks him "You ever kill a man yourself, Canton?" He responds with a demonstration. The "Nguyễn Văn Lém" allusion is an interesting idea, one I never thought of, but I think that might be stretching it. Perhaps not. As Year of the Dragon shows, Cimino's preoccupation with Vietnam extends well beyond The Deer Hunter.

1. I believe the woman who killed herself was the wife of the settler whose legs were crushed by the wagon during the battle. If I remember correctly she shoots her husband to put him out of his misery and then kills herself because she has nothing left to live for. Personally I never liked the suicide scene. Cimino went overboard to make the climax as tragic as possible. I like Heaven's Gate and think it is much better than its reputation suggests, but it has some truly bad moments like that one that keep it from being a great movie.

2. In the movie the government supported the Stock Growers Association in their plot to kill the suspected rustlers. The film suggests that the President of the United States had advanced knowledge of the invasion of Johnson County and gave his approval. There's no historical evidence for that, but in reality Wyoming's acting governor and senators were suspected of knowing and abetting the wealthy stock growers' plans. As depicted in the movie, the Wyoming National Guard received orders prior to the invasion that prevented them from helping the settlers. When the invaders were besieged by hundreds of angry settlers they sent out a messenger to alert their political allies of their desperate situation. Wyoming's governor sent a telegram to President Benjamin Harrison, who ordered the US Cavalry to intervene. Johnson County sheriff William "Red" Angus allowed the cavalry to take the invaders into custody on the condition that they be tried for their crimes by civilian authorities. However, all charges against them were eventually dropped.

3. Yes, Sam Waterston's character was out for revenge.

4. The man Waterston killed was one of the suspected rustlers on the death list. Waterston shot him to prove to Christopher Walken's character that he could personally kill a man.