Since the financial crisis in 2008-2009 China has shown a new assertiveness internationally, contradicting Deng Xiaoping’s earlier strategies of China to lay low internationally and develop economically. This new assertiveness is an often-discussed subject and is often connected to the Chinese rise and a presumed pursuit of regional hegemony in South East Asia, rejected by Chinese officials. This paper aims on studying China’s new assertiveness on both a systemic international politics level and on foreign policy level to understand what drives this new assertiveness. Graham T. Allison used three explanatory models to examine the decision-making during the Cuban Missile Crises, and I have adapted his three models to China’s behaviour in South East Asia and complemented them with e.g. factors that affect decision-making and contemporary theories of hegemony. Using this method gave me the opportunity to challenge the notion of a Chinese pursuit of hegemony since the case of China contained several anomalies compared to the theoretical framework, which instead points to an All-under-Heaven system emphasized by Chinese officials and scholars. The new assertiveness is explained mainly trough enhanced militarism, PLA influence and capacity, kept non-confrontational through e.g. Confucianism and Deng-ist advocates