The CW is gearing up for its epic four-night DC universe crossover event, and its doing so by releasing new posters and teasers for the "Invasion!" saga. In addition to the interlocking posters and new promo that dropped earlier this week, the network has released a new video that shows that this isn't the first time the Dominators have tried to conquer Earth.

The retro-style video jumps back in time around 70+ years and shows an early 20th century army using their guns and missiles to try and stop the conquering alien force. It doesn't work so well for the army, although viewers do get to see the extraterrestrials up close in this spot.

CLASSIFIED: We are not alone. The Invasion begins Monday at 8/7c on The CW. #DCWeek pic.twitter.com/d3Ye2roXiS— Legends of Tomorrow (@TheCW_Legends) November 22, 2016

The episode will also feature the reveal of exactly what future Barry Allen told Martin Stein (Victor Garber) and Jax (Franz Drameh) earlier this season on "Legends of Tomorrow." During a visit to the "Legends" set, Garber revealed that the message "sort of comes out in dribs and drabs. It’s a big mystery and a big deal. It’s a spoiler if I give you too much information, but it’s just part of the whole mystery of time travel and the fact that this is coming from Barry years later and then when he finds out — and that all happens in the crossover, so it just sort of unfolds as these things do on these shows, and lots of things occur in that time period.”

Starring Melissa Benoist as the Girl of Steel, “Supergirl” airs Mondays at 8 pm ET/PT on The CW. The network is also home to Grant Gustin as the Scarlet Speedster in “The Flash,” airing Tuesdays at 8 pm ET/PT, Stephen Amell as the Emerald Archer in “Arrow,” airing Wednesdays at 8 pm ET/PT and Victor Garber, Brandon Routh and Caity Lotz in “DC’s Legends of Tomorrow,” airing Thursdays at 8 pm ET/PT.