1940s
The 1940s decade covers the period from 1940-1949.

This decade on Earth is marked by World War II. Germany under Nazi rule has fronts against England and the USSR. With the attack on Pearl Harbor, the USA enters the war from which they emerge victorious and are established as a world superpower for centuries to come. Harry S. Truman becomes president after the death of Franklin D. Roosevelt and remains in office during the decade. In two alternate timelines, the outcome is radically different, with Nazi Germany conquering much of the world.

The end of WWII is followed by the Earth Cold War, which lasts until the late 1980s. 

Not surprisingly, scientific breakthroughs on Earth are centered on warfare, such as heavy water experiments, the atomic bomb (utilizing the principles of nuclear fission and/or nuclear fusion), and the V-2 rocket. 

In the field of art and entertainment, the films For Whom the Bell Tolls and Abbott and Costello Meet Frankenstein are released, along with stories featuring Dixon Hill. Songs released in this era include "Moonlight Becomes You", "How High the Moon", "My Old Flame", "Out of Nowhere", "Let's Get Away from It All", "It Can't Be Wrong", "That Old Black Magic", and "You're Nobody 'til Somebody Loves You".

Time travelers who visit Earth during this period precipitate the Roswell Incident. ()

Years

Events 
 World War II rages on Earth. (; ; ; et al.)
 In an alternate timeline, Edith Keeler is saved from the traffic accident by Leonard McCoy, allowing her to continue striving for her goals of world peace, which ultimately delays the the United States of America's entry in World War II. As a result of these actions, Germany is allowed to complete its heavy water experiments and this enables them to be first in developing of the atomic bomb. This, together with the V-2 rocket, enables Germany to capture the world. ()

de:1940er
es:Década del 1940
fr:20ème siècle#Années 1940
it:Anni 1940
nl:1940s
sv:1940-talet