We're up to the 1950s, the time of the Cold War, when the US and the Soviets were trying to get just about the whole world to align themselves with one or the other. This wasn't just about political power – it was also about economic systems – capitalism vs. socialism.
Arab Nationalism, from the outset, carried a socialist ideology. Experiences under colonialism had convinced Arab intellectuals and nationalists that democracy, as imported from the west, was "nothing more than a way to facilitate corruption and preserve a ruling class that would advance western interests over the interests of the local populations" (Houri, Walid). Arab Nationalism developed, in part, as a response to the social and economic changes that came from the colonial and early post-colonial period.
In 1952, Mohammad Naguib led the Egyptian Revolution that overthrew the Egyptian monarchy. Two years later, Gamal Abdel Nasser overthrew Naguib's government and became president. As Egypt's new president, Nasser refused to align with the US. So what did the US try to do? Isolate Egypt from the rest of the Arab states by bringing them all onto the side of the United States. What did Nasser do in response? He tapped into Arab nationalist ideology to turn all the Arab countries against the US. While he did not fully succeed, Egypt's powerful stance against the West produced rapid growth in the spread of Arab nationalism. People throughout the region started believing in the future of a single, United Arab State. Nasser's socialist program and populist platform further inspired people to identify with this growing movement.
A few years later, in response to Israel's import of arms from the French, Nasser secured Soviet arms in what was the first Soviet intervention into Middle East politics. The result? The West lost monopoly over the region, shifting power considerably. This move was seen as a victory by Arab nationalism over Western imperialism. Soon, Arab nationalism became the "uncontested ideological force of the Arab world, Nasser its uncontested ruler" (Dawisha, Adeed. Arab Nationalism in the Twentieth Century).
Wait a minute – ideology doesn't grow by itself. What else led to the rise of Arab nationalism? Well, modernization and globalization lent a hand. The post-WWII era was a time of major shifts in traditional values, customs, and systems of authority throughout the Middle East. With the fall of the Ottoman Empire, new spaces for leadership, organization, and loyalty opened up that Arab nationalists filled. Modernization and mass media enabled Arab nationalism to reach parts of the region previously isolated. Egypt controlled most of the region's media at that time, and the onslaught of messages for Arab nationalism won the people's hearts and minds. So much so that it threatened the authority of certain heads of state . . .