1930s

[edit] Years

Civil war breaks out on the planet Xindus. (ENT: "The Shipment")
The Nazi movement, led by Adolf Hitler, takes power in Germany and throughout the decade turns the country from a democracy into a brutal dictatorship, eventually leading to the breakout of World War II. (TOS: "The City on the Edge of Forever")
In an alternate timeline, Edith Keeler is saved from the traffic accident by Leonard McCoy, allowing her to continue striving towards her goal of world peace by founding one of the largest peace movements in the United States. By the late 1930s, the growing pacifism caused by this movement and others, would cause the United States to focus on diplomacy and ultimately delay its' involvement in World War II. (TOS: "The City on the Edge of Forever")