Generating and projecting aerospace power in the 21st century are technologically complex, requiring a myriad of different skills. Recruiting, training, and retaining people with the necessary mix of skills are major challenges for the U.S. Air Force's personnel community. With the end of the Cold War, the United States armed forces began to implement a substantial reduction in total personnel, or end strength. The Air Force, for example, went from a total end strength of 571,000 in 1989 to 368,000 in 2002, despite the fact that it was involved in numerous crisis deployments, including major operations to liberate Kuwait, stop Serbian operations in Kosovo, and after 9/11, pursue parts of the war on terror in Afghanistan and Iraq. All of these events left the Air Force with severe manpower problems at the beginning of the 21st century. Many career fields were understrength. Authorizations went unfilled, and many fields had severe skill imbalances, such as a dearth of middle-level people.