The first use of air power was for reconnaissance, or recon for short. Basically recon meant the inspection of an area to gather military information. It basically involves spying on the enemy's military and patrolling an area for enemy movement. Balloons were initially used as airborne platforms to provide observation of enemy-troop movements in several 19th-century wars. However when airplanes were invented they became the tools of choice for recon. This was because planes were more agile and quicker. Because planes could travel as the bird flies, there are no barriers to stop them from proceeding into enemy ground, apart from other planes. At that time when planes were first beginning to be used there were few other planes, and the eye was the only way to detect other planes. Since the plane was also the fastest vehicle and the pilot could see all the surroundings around him from a high altitude, this made the airplane the perfect tool for recon.

The importance of aerial reconnaissance made it clear that the belligerent able to spy on the enemy from above the battlefield would enjoy enormous advantages. This realization led to the emergence of fighters as a distinct category of aircraft. The fighter would not only protect friendly reconnaissance aircraft, but would also shoot down enemy reconnaissance aircraft. As you can see aerial reconnaissance lead to aerial combat.

Once radar was invented reconnaissance using aircraft became impractical. This is one of the things that spurred the development of stealth aircraft. With stealth aircraft the airplane could once again gain its freedom to go in to enemy territory undetected. However with the invention of modern satellites the need for reconnaissance using aircraft was no longer needed since the satellites provides a less dangerous alternative for reconnaissance.