So far, the triangles remain true UFOs. They may very well be man made, but we don't know that, not yet. Even if they are man made, there are a lot of mysteries surrounding the triangles. One being: are the triangles based on alien technology? If not, it is still an incredible creation; these triangles are huge and incredibly fast, even downright spooky. What is their purpose? They've been around for decades, why the continued secrecy?
If the triangles are man made (either the U.S. or some other nation) and are flying in the skies of the world, as they clearly are, are they doing so with the complicity of other governments? Or is there just one, or a very few, governments having their way with the rest of the world? In this scenario, we hardly need aliens here, we seem to be doing a good enough job on our own involving issues of deceit, subversion, secrecy, disinformation, and agendas.The triangles appear all over the world, which means they appear in international air space; the abrupt appearance of an unknown craft in another country's air space seems dangerous. And if the craft is astoundingly fast, as the triangles appear to be, and their origin is unknown (presumably) no harm can come to either craft or nation. If a black triangle appears in China, who would China respond to?
The triangle sightings continue, and have been occurring for so long and the fact remains, Alien or man made, almost doesn't matter, because the phenomena of the triangles is so weird (decades long event, fantastic speeds and manoeuvres, odd effects upon witnesses, global appearances, secrecy, etc.) the topic stands on its own as a fringe object of study.
