List of countries where it is known or suspected the US has covertly corrupted and/or interfered in democratic elections since 1945 [in no particular order].
Italy (1948), Bulgaria (1990), Albania (1991), Indonesia (1958), Grenada (1984), Nicaragua (1989), El Salvador (1960, 1992), Brazil (1962), Honduras (1980), Venezuela (2004)
List of countries where it is known or suspected the US has backed military coups, encouraged civil unrest, invasions and/or bombed to overthrow (or attempt to overthrow) democratically elected governments.
Iran (1953), Guatamala (1954,1983), Guyana (1964), Chile (1973), Bolivia (1967), El Salvador (1962, 2004), Ecuador (1963), Greece (1949,1967), Venezuela (2002), Equatorial Guinea (2004), Fiji (1987), Nicaragua (1989), Dominican Republic (1965), Brazil (1964), Iraq (1963)
Of course the US has (post-WWII), interfered in the affairs of and invaded many other countries, (70 of the world's nations in fact), but not all of them were fully functioning democracies at the time although US actions certainly prevented some of them from becoming democracies.
Dictator run countries either currently backed by the US or at one time or another in the past.
Saudi Arabia, Iraq (Saddam Hussain), Iran (the Shah), Chile (Pinochet), Kuwait, Panama, South Korea, Pakistan (General Musharraf), Phillipines (Ferdinand Marcos), Jordan, Lebanon, Cambodia (Pol Pot!!), Zaire, Brazil, Indonesia (Suharto), Haiti, Cuba (Batista), Nicaragua (Somoza), Costa Rica, Argentina, Uruguay, El Salvador, Honduras...
The US has also backed a number of other brutal opposition groups, notably.
The Taliban, Mujahideen, Guardia.... I could go on but...
If this isn't enough for you and you don't think the US engages in terrorism, read this.