The early 20th century witnessed the ideological triumph of Arab nationalism and pan-Arabism in the Middle East with the cultural and literary renaissance that rose in the region leading to a collective consciousness as to the Arab identity among Arab intellectuals. It was the Arab nation-identity rather than the individual Arab states' identity that shaped the political discourse of the then-Arab regimes. In addition, the political juncture with the advent of anti-colonial movements in the region following the Second World War set the stage for the radicalization trend of the military regimes which aimed to unify Arab nations under one state and carry out sweeping economic programs of modernization and centralization. On the other hand, the defeat in the Arab-Israeli War of 1967 was a defining historic moment in the reconfiguration of Arab politics in the Middle East. Since the war, Arab states moved into a post-nationalist stage in which strict ideological control and authoritarian policies were replaced with a set of limited political and economic openings and the Arab-Israeli treaty. This article investigates the birth and rise of the Arab nationalist movement along with the ideological origins of the radicalization trend of the ruling regimes in the Middle East. The article suggests that pan-Arabism, Arab socialism and anti-imperialism gained momentum in the 1950s and 1960s with a number of political developments under Egypt's President Abd-al Nasser. Nevertheless, the eventual decline of the radical regimes was witnessed with the 1967 Arab defeat that inflicted a mortal blow to the Arab nationalist movement. From 1967 onwards, the regimes lost both their capability and aspirations to realize Arab nationalist goals and in this era, state nationalism came to the forefront.