Why did Eisenhower authorize the CIA to overthrow a democratically elected leader (Mohammad Mosaddegh) in Iran?

The US and UK did not want Iran to be a developed or successful country so they did everything in their power to keep Iran form progressing, including destroying their democratically elected government under the leadership of Mohammad Mossadegh. Mossadegh had already nationalized Iran's oil and so the US and UK saw this as a threat and eliminated him.