Overthrow #7 : Iran
Ah yes, in with the Cold War and unfortunately for any nationalistic country intent on getting fair profits from their natural resources- enter C.I.A.
The British were full-on exploiting the Iranians for their oil, only giving them (at most) 16% of the profits from their oil (nearbye Middle Eastern countries had deals giving them 50% w/ the Americans). Mossadegh was elected in 1951 and pursued two main ideals: (1) nationalizing their oil and (2) promoting democracy. Time magazine described him as the "Iranian George Washington". Unfortunately, both of his ideals went over very badly w/ the British and their monarch, Mohammed Reza Shah whose power was becoming increasingly ornamental.
The Take Over
First the British went for it. They tried to get rid of Mossadegh by blockading ports and attempting their own coup. After these failed, and their embassy was kicked out, Britain went to the Americans for help. Eisenhower had just been elected, and after some convincing (Britain played the Communist card even though Mossadegh disliked that ideology), the US embarked on its first covert C.I.A. overthrow.
The details here are very disturbing. The C.I.A. wanted to destabilize Iran, but this was extremely tricky since Mossadegh was very popular. To do it, they bribed Congressmen, religious leaders, and journalists to say and write negative things about Mossadegh. When that failed to do the trick, the C.I.A. paid off 2 Iranian operatives who had relations w/ street gangs to start riots around the city. In the middle of this C.I.A. induced chaos, the US's new selected leader (General du jour Zahedi) announced on Radio Tehran that he was the new leader. Soon after, Mossadegh resigned and went into house arrest.
The immediate ill effects, was the Shah taking charge and all pretenses to democracy being thrown away. Also, the US now had their foot in the door into the oil profits (20%). All of this, for obvious reason, embittered much of the public to the US and led to the 1979 Iranian revolution. Additionally, even though it is doubtful Carter would have tried to overthrow the new government, many Iranian feared they would which led to the hostage crisis. Today, we are still known as, "The Great Satan" in Iran and have horrible relations w/ them.
Ranking (Worst to Least Worst)
7. Puerto Rico
I'm putting Iran right on top. Like we saw in Cuba and Nicaragua, our success in getting rid of a Democratic leader resulted in a backlash government that was every Conservatives worst nightmare, in this case the religious fundamentalists that still rule Iran. Whether or not Iran would've remained a democracy is a hypothetical, but it cannot be argued that the US directly caused them not to be. That US attempts to import democracy to the Middle East today is met w/ cynicism, is hardly surprising. Additionally, this overthrow led to destabilization and anti-Americanism in the entire region. Not to mention today's problems with an Anti-Semitic American Hating President intent on gettin the bomb.