It was a combination of pressure from above and below: US pressure, but also a newly middle-class population starting to raise hell. In most of those countries, protests and civil unrest presaged the transition to democracy--and suppressing it would cost the government their US support, so the easiest thing to do was to just give in.
Sorry, but in Latin America, US pressure was to create the dictatorships, not to remove them. US helped to create them, and supported the torture and chasing of dissidents.
They did, yes, and then (as ertian described) they also exerted pressure to get the dictatorships to hold democratic elections, as long as that wouldn't imperil US access to markets.
Sure, in some countries and time periods. I'm not in any way saying the US has a flawless record. I'm just saying that US pressure was not the only reason why countries transitioned to democracy: it was a combination of popular and international (largely US) pressure. When one or the other was missing, the transition generally never happened.
