I am not really caught up to why this even started, but on September 20, a group of 2000 people headed out to raid Area 51. Their goals included finding aliens.
The raiders all used an evasion tactic called Naruto Running, presumably to dodge alien lasers. Memes also suggest that Beyblades and Minecraft torches were used to thwart the Area 51 guards.
The guards came with helicopters and a tank, though they were not used against the raiders as far as I know. The event was so popular, that even News channels broadcasted about it. In one of those News reports, you can even see a Naruto Runner. You can see this News report in the video below.
Personally, I have no idea why all this happened but I find it hilarious.