From FEMA - 

The NIMS community includes emergency responders and other emergency management personnel, federal partners, non-governmental organizations, the private sector, and elected and appointed officials responsible for making decisions about incidents.

Before NIMS, the emergency response community had long recognized the need for standardized incident management guidance, particularly when responding to major incidents that required collaboration among multiple organizations and jurisdictions. Key incidents such as Southern California’s 1970 wildfire season, the terrorist attacks on September 11, 2001 (9/11), and Hurricane Katrina in 2005, served as pivotal points for the nation to both recognize and reaffirm the need for a shared multijurisdictional, multiagency incident management system.

Since 2004, NIMS evolved through numerous iterations of guidance, resources, and tools. Now, more than 20 years after the tragic terrorist attacks on September 11th that drove the creation of NIMS, the threat of human-induced disasters also has only become more complex. As these hazards and threats evolve, the NIMS model continues to offer communities a flexible system for unified response to incidents of any type, level, or scope.