Congratulations on your decision to enlist in the United States Air Force! (Well, maybe you haven't actually made that decision yet, but you're reading this article, which means you must be interested.)
The Air Force is the youngest of our Nation's military services. It was created from the Army Air Corps as part of the National Security Act of 1947.
The Air Force is also one of the hardest services to join. Why? Well, it seems that the Air Force is the most popular of the military services. They have the highest reenlistment rate of any of the services. In other words, those who join tend to want to stay in after their initial term of service is up. This results in fewer slots for new recruits. In fact, over the past several years, the Air Force has found themselves in the embarrassing position of having more people on active duty than Congress says they can have. That means, each year, some people who want to stay in the Air Force, can't, and many people who want to join the Air Force can't.
That doesn't mean it's impossible to join. If you can meet the enlistment qualifications, and are willing to be very flexible in job-choices, and are willing to spend months (possibly several months) waiting for an enlistment/training slot, you can be among the 30,000 (or so) who will enlist in the Air Force this year.