In the annals of modern day UFO research, there are three important dates that come to mind.

(1) The first atomic bomb test, 7/16/1945 at the then Alamogordo Bombing and Gunnery Range near the town of San Antonio, New Mexico known as Trinity.

(2) The first modern day sighting of a UFO, 6/24/1947 by Kenneth Arnold while flying near Mt. Rainier, Washington.

(3) The Roswell Crash, 7/2/1947 where allegedly an extraterrestrial space craft crashed in the desert near Roswell, New Mexico.

With these dates in mind, it seems that the detonation of the first atomic bomb, which sent out seen and unseen radiation into space, caught the attention of extraterrestrial beings from beyond our solar system, which signaled that the human civilization had become capable of producing weapons of mass destruction. The Trinity test also made them aware that not only were we now able to destroy ourselves, but also may soon become capable of interstellar space travel as well in the coming centuries.