Pre WWI aviation had just started and only one in ten thousand people had even seen a plane fly. Air races and demonstration teams were popular in those days and would attract thousands and thousands of people.
WWI would see the aircraft blossom from an experimental curiosity into a fully fledged weapon of war. Pilots returning home would bring their skills and desire to fly with them.
The Inter-War period between WWI and WWII is known as the golden age of flight. During this time barnstorming was popular. People like Charles Lindberg, Amelia Earhart, and Wiley Post would set dozens of records. In my opinion some of the most practical and beautiful aircraft ever built came out at this time. The birth of the Airlines started at this time.
WWII would generate a dramatic increase in aircraft performance and would see the rise of the Jet age.
The post war period would see a sharp decline in military aviation but as pilots came home again a silver age of flight. Most of the general aviation aircraft of this period became popular and are still being flown today.
Since then aviation has been gradually eroding away. The cost of flying has skyrocketed and participation has plummeted. Worse, the cost of learning to fly is also on the rise.
I think the largest determining factor is the ever increasing regulation by the federal government. Flying isn't the simple joy that it was. Most large airports are choked with commercial traffic. The smaller airfields have been vanishing from the map one by one.
In recognition of this the FAA has created the Ultralight category. Simply put, if your aircraft meets certain requirements you do not need to register it or have a pilot's license to fly it. This has been a boon for folks who just want to fly. More recently the FAA has created the Light Sport category. These aircraft are bigger and more capable than ultralight but have limitations over fully fledged certified aircraft.
Those aviation enthusiast left among us should petition and push for the continued deregulation of flying. Fewer laws, not more. Fewer restrictions on airports too. Put aviation back in the hands of the weekend pilots.
I do see some promise in the areas of ultralight aviation, light plane aviation, and sailplane flying. These folks are finding ways to fly with 'garage technology' and doing it on a budget that any working person can afford. This will be what keeps aviation alive.
If you would like to see the kind of flying I speak of check out http://m-sandlin.info/
Mike Sandlin has captured the spirit of flight in a safe, responsible, and affordable way. Furthermore, he has made his technical drawings freely available to the public. I had the great honor of contributing to the 'Airchair' community in 2003 by creating the very first X-Plane simulation of one of Mikes design's the BUG (basic ultralight glider). In the years since I'm happy to say that Airchair flying has gained popularity gradually. It may in fact be the only corner of aviation that is growing.
Why is it growing? Well it's fun, affordable, and best of all largely unregulated.