Terrorist groups in the Middle East continue to pose a challenge to U.S. interests and a threat to the security of the United States and its allies. It is important to understand what factors drive the behavior of these groups and how they adapt to certain challenges. The Islamic State of Iraq and al-Sham (ISIS) is a unique terrorist organization that has had an indelible impact on the Middle East and continues to pose a threat to U.S. interests. Examining ISIS's behavior and development over time will help illuminate how certain types of decisions are made in a terrorist organization, what consistencies are present in decision-making, what motivates the behavior of terrorist groups in conflict, and when or why an organization might modify or amend its doctrine to adapt to certain challenges. In the case of ISIS, how the group has adapted or remained consistent in its use and reliance on violence, local support, and apocalyptic ideology is examined. Examining those areas of ISIS's behavior over time help illuminate if and under what conditions the group has been compelled to alter its approach. Findings help us understand what (if any) factors have forced the organization to shift its behavior over time in order to help it advance its stated ultimate goal of a restructured united, global Muslim society ruled by a purely Islamic state system, unadulterated by non-Islamic ideas, morals, or legal concepts.Terrorist groups in the Middle East continue to pose a challenge to U.S. interests and a threat to the security of the United States and its allies. It is important to understand what factors drive the behavior of these groups and how they adapt to certain challenges. The Islamic State of Iraq and al-Sham (ISIS) is a unique terrorist organization that has had an indelible impact on the Middle East and continues to pose a threat to U.S. interests. Examining ISIS's behavior and development over time will help illuminate how certain types of decisions are made in a terrorist organization, what consistencies are present in decision-making, what motivates the behavior of terrorist groups in conflict, and when or why an organization might modify or amend its doctrine to adapt to certain challenges. In the case of ISIS, how the group has adapted or remained consistent in its use and reliance on violence, local support, and apocalyptic ideology is examined. Examining those areas of ISIS's behavior over time will help illuminate if and under what conditions the group has been compelled to alter its approach over time. Findings will help us understand what (if any) factors have forced the organization to shift its behavior over time in order to help it advance its stated ultimate goal of a restructured united, global Muslim society ruled by a purely Islamic state system, unadulterated by non-Islamic ideas, morals, or legal concepts.Understanding how terrorist organizations behave is not only an academic goal, it also has important implications for U.S. national security strategy and foreign military operations. According to the U.S. National Security Strategy, the U.S. seeks to prevent any potential threats to national security such as attacks to the homeland as well as any threat to U.S. interests in the Middle Eastern region to include U.S. allies, resources, military personnel, as well as U.S. citizens abroad. The United States continues to combat present terrorist organizations and strives to deter future organizations from developing and evolving. As the U.S. supports its allies and partners in the region, these organizations