The UFO phenomenon is recorded throughout history but the sightings were off the chart after Hiroshima. However it's a little more complex than that, as by many definitions we're just as alien as the rest of the universe who have been tipping up here practically forever if not longer than the monkey. As Bob Dean explains.
It's the greatest story in human history.
The full documentary is here but yes; the bombs aren't allowed and that's why we haven't nuked ourselves yet. Quite a few tried.