The U.S. Army experience in Bosnia, during the 1990s, had a tremendous influence on how the army later operated in Iraq. After the Cold War ended, the army was looking for what it should prepare for next. There were no more major foes to prepare for. Aside from North Korea, Iran and Iraq, there were no major potential opponents out there. In response, many army officers set their sights on peacekeeping. Then, when the breakup of Yugoslavia created a Balkan civil war in the 1990s, the army eventually got sent in as peacekeepers.
Army troops had never really trained for this, and had to make it up as they went along. But they had one major advantage. Since the early 1980s, the army had been constantly raising its standard for new recruits (both troops and officers.) The impact of this was seen during the 1991 Gulf War, and in the Balkans, a few years later, the troops were just as energetic and innovative. But that turned out to be a problem. Rather than helping the Bosnians to do a lot of things, the troops just went ahead and did it. This included establish police services, reconstruction and aid distribution. Put too many U.S. troops into an area, and they'll but the locals out of work. This had a tremendous influence on strategy and tactics used in Iraq.
Over 100,000 American army troops went through the Balkans in the 1990s. As a result, there was hardly a battalion in the army without at least a few Balkan vets. When the army went into Iraq, the Balkan experience was still fresh. It became obvious early on that what worked in the Balkans, would work in Iraq. It was in the Balkans that U.S. troops got their first taste of raids, checkpoints, irregular warfare, hostile civilians and police work. Hardly anyone in the media caught this connection, but among the troops, the Balkan experience was often a lifesaver, and provided a useful template on how to most effectively work with Iraqi civilians.
American troops displayed an enormous amount of ingenuity in dealing with the situation in Iraq, and most of these exploits will only be recognized in the history books. While the troops themselves deserve most of the credit, some goes to the Balkan experience, which served as a training experience for the far more hostile Iraq campaign.