Starting in 1962 the CIA begins interfering in Chilean elections, turning in 1964 to incubation of the military junta that in 1973 put Augusto Pinochet into power after a CIA backed overthrow of Salvador Allende (having failed to buy his opponents elections and a failed coup attempt in 1970, among others). Salvador's government was replaced by a military dictatorship that suppressed and brutalized the country until 1990, with full US knowledge and complicity, and included assistance in the murder of political opponents. Allende's crime:

"Allende then proceeded towards strongly socialist policies based on his electoral victory, including a prices freeze, an increase in wages, nationalisation of the coal and steel industries, nationalisation of the main foreign copper firms, and of 60% of the private banks (Skidmore & Smith 2001, p127; Hudson 1994). Almost 500 firms would be nationalised (Hudson 1994). Workers often took the initiative, occupying the offices of foreign firms such as ITT and Ford until they were nationalised - this led to a partial financial blockade by the U.S., as well as the withholding of loans from the World Bank, the Inter-American Development Bank, and the U.S. Export-Import Bank (Skidmore & Smith 2001, p127)."

--James Ferguson, The Struggle for Democracy: Chile and Argentina

The US was supporting "anti-communist" factions in Chile as early as 1950. CIA activities recieved significant funding from the business community (allegedly Pepsi, from what I've read).

The AFL-CIO was also involved, continuing its long history of working against foreign labour unions. [1]

Salvador Allende was the worst possible scenario for a Washington imperialist. He could imagine only one thing worse than a Marxist in power-an elected Marxist in power, who honoured the constitution, and became increasingly popular. This shook the very foundation stones on which the anti-Communist tower was built: the doctrine, painstakingly cultivated for decades, that "communists" can take power only through force and deception, that they can retain that power only through terrorizing and brainwashing the population.

After sabotaging Allende's electoral endeavor in 1964, and failing to do so in 1970, despite their best efforts, the CIA and the rest of the American foreign policy machine left no stone unturned in their attempt to destabilize the Allende government over the next three years, paying particular attention to building up military hostility. Finally, in September 1973, the military overthrew the government, Allende dying in the process.

They closed the country to the outside world for a week, while the tanks rolled and the soldiers broke down doors; the stadiums rang with the sounds of execution and the bodies piled up along the streets and floated in the river; the torture centers opened for business; the subversive books were thrown into bonfires; soldiers slit the trouser legs of women, shouting that "In Chile women wear dresses!"; the poor returned to their natural state; and the men of the world in Washington and in the halls of international finance opened up their check-books. In the end, more than 3,000 had been executed, thousands more tortured or disappeared. [2]