With a promise to nationalize Chile's copper mines, banks, and largest industries, as well as break up its landed estates, Salvador Allende won less than 37 percent of the vote in a thee-way 1970 presidential race. Although opposed by almost two-thirds of the voters, he was still expected to occupy Chile's White House, the Moneda: Chilean law called for the Congress to select the president when no candidate had won a clear majority. And historically, the legislature always voted for the man who had garnered the most votes. Thus, Allende, leading a leftist coalition, the Unidad Popular, would win.

Fearing that Allende might convert Chile into a bastion of Marxism, the vehemently anticommunist U.S. president, Richard M. Nixon, ordered Secretary of State Henry Kissinger, to do something. Kissinger complied: Without informing Edward Korry, the U.S. ambassador to Chile, he encouraged the Central Intelligence Agency (CIA) to...