In 2011, the world was taken by surprise by the Arab Spring and, subsequently, by its different outcomes. This thesis aims to explain why some countries of the Middle East and North Africa (MENA) region remain stable, while other experience civil wars when faced with uprisings. It formulates the main hypothesis that countries that were US-aligned during the Cold War are less likely to experience civil wars following an uprising. A careful analysis of alliance patterns revealed that all Soviet-aligned countries have experienced at least one civil war or a revolution since the end of the Cold War, while all US-aligned countries have remained largely stable. It thus seems that the transition from a bipolar system to an American-led unipolar system of international relations still has consequences and is relevant to explain developments taking place in the MENA region. To understand the mechanisms at play, three sub-hypotheses were formulated to explain the different scenarios observed after the Arab Spring: U.S.-aligned countries with U.S. support remained stable (Bahrain); U.S.-aligned countries without U.S. support experienced regime change but no civil wars (Egypt); Soviet-aligned countries without U.S. support experienced a civil war (Syria). A thorough analysis of the way events unfolded in each country revealed that 30 years of alliance with the superpower made Bahrain and Egypt's security forces exceptionally resilient and ready to cope with uprisings, while 30 years of isolation made Syria more prone to civil wars. It also revealed that the U.S. made several mistakes in the way it handled the Arab Spring, and other powers such as Russia and Iran managed to take advantage of the situation. This could point to an end of U.S. supremacy in the MENA region and the beginning of a brand new order of international relations.