Although the CIA pioneered the use of larger, armed UAVs, the American intelligence service has been ordered to reduce its armed UAV activity and let the air force and army handle it, especially the use of armed UAVs in counter-terrorism operations. The CIA still uses a lot of larger UAVs for reconnaissance and general information collecting but the use of armed UAVs is now largely a Department of Defense monopoly.
"Medium" UAVs (weighing from a few hundred pounds to a few tons) have been around for decades, and achieved an acceptable degree of reliability by the 1990s. Then came advances in electronics that provided excellent day and night cameras, and the ability to stream the video live to users anywhere on the planet. In the early 1980s, the 48 kg (105 pound) laser guided Hellfire missile entered service. By the 1990s, you could now mount a laser designator on one of these UAVs, along with the Hellfire, and in 2001, at the urging of a U.S. Air Force general, a Hellfire was launched from a Predator UAV for the first time.
The Predator was a recently developed, one ton, UAV, created with the help of Israeli UAV designers. The Israelis had taken the lead in UAV development since the 1970s, but the U.S. military was not inclined to buy from foreigners, especially since the air force wasn't keen on aircraft that did not require pilots. Then September 11, 2001 came along, and the CIA sent some of the Predator's it already owned to Afghanistan, and was the first to use a UAV fired Hellfire in combat. Over the next seven years, as more Hellfire armed Predators got into combat, the Hellfire became more successful, and more popular with the troops on the ground.
At the same time the Predator first fired a Hellfire, the manufacturer realized what they had, and began developing a larger UAV, that could carry more weapons. The Predator could only carry two Hellfires. But the larger Predator B, eventually to be called the Reaper, could carry a ton and a half of weapons. This would include GPS guided (JDAM) 227 kg (500 pound) bombs. This put the UAV in direct competition with fighter bombers (like the F-15, F-16 and F-18). This was anathema to the air force generals, and although the Reaper first flew in 2001, it didn't get into combat until 2007. Reaper was an instant success, and the resistance within the air force began to melt.