There have been UFO sightings at least since the end of WW2. There are some indications that they appear in Ancient Art as well.
That must be one hell of a “Prime Directive” they have in place.
If they weren’t going to intervene in WW2 or the subsequent threat of Nuclear Annihilation, who really cares about them anymore.
They had thier chance to “serve man”.
‘They’ are waiting for a ‘ONE WORLD GOVERNMENT’ to emerge, so that they won’t have to deal with all the separate ones..................