The proximate cause of the coup that ousted King Farouk was the drubbing that Egypt, along with every other Arab state, had received at the hands of the Israelis during the 1948 Arab-Israeli War. The officers blamed Egypt’s corrupt monarchy, which was totally under British control anyway, for the defeat (when the 1967 Six Day War rolled around, and Israel throttled the Egyptian army again, you can imagine that this was kind of an embarrassment for Nasser), and, in a rare bit of Cold War collaboration, their feelings were encouraged by both the US and USSR, who didn’t much care for the fact that Britain had so much control over the Suez Canal. They organized protests against and attacks on the government, while building support for a coup to replace Farouk. They began the coup on July 22, after Naguib found out that Farouk knew who the Free Officers were and that he was planning on arresting the lot of them. That evening was spent consolidating their support, including crucially the Muslim Brotherhood, whose leaders had been approached by Nasser himself and agreed it was time for the king to go.