You could reel yourself a World Government in on the back of a lie this big if you were able to pull it off. Don't think people are this stupid? See my previous post below. It would be the last word in mass distraction from real problems.
Our alien science is so advanced it defies your comprehension. But what we really need are nice warm wool shirts.
They Need To Attack Our Combustion Engine Flying Machines ... to test their starship propulsion systems against our benchmark!
Limeys seeing'em everywhere ... common before a World War starts, historically ...
Are they Time Travelers getting a peek at our 21st century civilization right before it gets nuked? I dunno. Some people think it is something more sinister.