Supergirl arrive in Central City

She does not come alone, Green Arrow and The legends come to help Flash to fight the dominators. We were informed by nearby sources that these evil creatures had already come to omit he earth but a treaty of peace was made. 

The operation known as the Advanced Aerospace Threat Identification Program was the creation of former Senator Harry Reid,

former leader of the Democratic majority in the Senate.

Reid represented the state of Nevada, the site of several reports of UFO sightings and home to the mythological "Area 51", a top secret base of the US Air Force,

whose hangars supposedly hide the remains of extraterrestrials captured by the army, according to believers in theories of an alien conspiracy.