How did Vietnam and Watergate shape American perception?

They made everyone more cynical meaning they were involved in themselves and didn't care for superheroes that much and that there wasn't use to them. Due to this, they made the superheroes more exaggerated  and theatrical. This changed on 9/11 because due to a threat from outside the country, people were scared and needed superheroes again.

c) troops march forward in close formation against newer, more accurate weapons

an era of negotiation.

is that an answer to your question?