Very biased film
All the left wing people are portrayed as the good guys when in fact Allende and his Popular Front were hard-nosed Marxists prepared to transform Chile into a full-blown Communist state, even though at the last election they had only 43% of the vote. In other words the majority of Chileans did not want to become a Marxist state. When Allende began moves to form and arm a 'popular militia' of peasants and workers the military had no choice but to step in and defend the country. It's entirely owing to Pinochet and the other members of the Junta that Chile is a democratic state today.
This is a very one-sided film and there are always two sides to a story. As for American involvement of course there was. It was definitely in the interests of the United States that Chile should remain a democratic nation.
Count on it, if Allende had stayed in power and established his Peoples Army we'd have seen just as many dead bodies in the streets, they would just have been middle-class bodies instead.