Consider this timeline beefore 1940 there were few UFO reports. Then:
1945: Atom Bomb created and used as a weapon
1946: many UFO sightings
1948-1951: More UFO sightings
1952: UFOs stalking Whitehouse - contact was made
1953-1970: Less UFO sightings.
I agree with Krusten.
We might have sightings before '45, but we simply have yet to recognize it as UFO.
Maybe some farmer somewhere saw some strange flying object but he paid it no mind.
Or maybe some citizen in Roman empire saw strange flying object but they thought it was Jupiter/Zeus came visiting.
I was actually having this conversation with a friend the other day!
He is convinced that we have met at least alien technology, and that is what caused such a massive technological explosion for us. Considering a 100 year gap between, say, 1820 and 1920 there was some technological advancement, quite a bit, but nothing super extraordinary really. You had the automobile, but what is that but a horseless cart? Then, 1920-2020. We went from massive radios, to computers that took up entire buildings and had about as much memory power as a cheap pocket calculator, now we have one device in our pocket that does EVERYTHING.
I do think there is a correlation.
I must respectfully disagree that UFOs directly corelate with nuclear weapons. This is merely a coincidence, as others have pointed out.
Before human flight was possible in the beginning of the 20th century, there were only a handful of (Grounded) science fiction books written in the later half 19th century that fantasized about humans traveling to distant planets by means of a "Ship." Aliens were also an idea, but in that time they were a fringe group interest, like Lovecraftian & SCP entities are today.
What I'm getting at here, in a more detailed explanation than others, is that the thought process of pre-atomic era humans was that UFO were entities of God(s) and the heavens, and not something that was technologically achievable by mere mortals. Pre-modern UFOs were seen as angels, and perhaps at times as demons.
Identifying UFOs as what they are and not as superstitiously explained away religious occurances is a result of the technological advancement of culture at the time, that coincidently lead the ability to manipulate the atom.
This I address to Xaphandart specifically..
I have more than a doubt that aliens assisted humans through technological progression. I have a logical mind against the likelihood.
The cause of our rapid advancement the last 100 years is a side effect of compounding knowledge; think compounding interest if you're economics minded.
Until the invention of the printing press in the 15th century, humanity had no efficient way of mass recording information from collectively gained experiences. Since the time of that invention, humanity's recorded and (More importantly) available knowledge has been growing at a compounding rate.
If you understand math, you may be starting to see why there has been exponential growth in technological achievements ever since the end of the middle ages.
If you don't understand math, I'll try to briefly explain. Because of the printing press, books, newspapers, and pamphlets could be printed and copied at well over twice the speed it would have taken someone to hand write them. In fact it was more than double of double the speed. I hope you understand, dear reader, by this example that means 4 books could be written in the time that 1 would have taken. This meant back then that 4 people could read about the same material at the same time, instead of just 1 person. Hence, people just simply become more educated. This is a gross oversimplification, but you get the picture.
This is what enabled many future advancements over the next few hundred years. More printing presses were made because more people were smart enough to make them. More improvements on the printing press were made because people were smarter, so now instead of 4 people, it was 16 people learning the most recent and up to date materials.
Finally, towards the dawn of the 20th century, we had a collective amount of enough educated people that were so smart they created a printing press that could print to itself. This was the first modern computer.
The computer did what the printing press did, but it did it at 1000x the speed because it was so advanced it was (Gross oversimplification) like having 1000 printing presses working within the time it would've taken the very first one that Johaness Gutenburg invented 500 years before.
Today we have computers so much more advanced than the first one, that they are recording information at such a speed that it would be like a billion people publishing a billion new books EVERY DAY. Hence, I am doubling back to my point here…
We are recording information so quickly, and sharing it so quickly with everyone, that our realm of readily available knowledge is a trillion times larger than it was 600 years ago when the printing press was first invented. Frankly, it's impressive that humanity isn't more advanced by this point.
JG would be both proud and terrified of his achievement.