Here's a short story:

Operation Barbarossa (German: "Unternehmen Barbarossa") was the code name for the Axis invasion of the Soviet Union, starting Sunday, 22 June 1941, during World War II. 

The operation stemmed from Nazi Germany's ideological aims to conquer the western Soviet Union so that it could be repopulated by Germans, to use Slavs as a slave-labour force for the Axis war-effort, and to seize the oil reserves of the Caucasus and the agricultural resources of Soviet territories. 

In the two years leading up to the invasion, Germany and the Soviet Union signed political and economic pacts for strategic purposes. Nevertheless, the German High Command began planning an invasion of the Soviet Union in July 1940 (under the codename Operation Otto), which Adolf Hitler authorized on 18 December 1940. Over the course of the operation, about four million Axis personnel, the largest invasion force in the history of warfare, invaded the western Soviet Union along a front. In addition to troops, the Wehrmacht employed some 600,000 motor vehicles, and between 600,000 and 700,000 horses for non-combat operations. The offensive marked an escalation of the war, both geographically and in the formation of the Allied coalition. 

Operationally, German forces achieved major victories and occupied some of the most important economic areas of the Soviet Union, mainly in the Ukrainian Soviet Socialist Republic, and inflicted, as well as sustained, heavy casualties. Despite these Axis successes, the German offensive stalled in the Battle of Moscow and subsequently the Soviet winter counteroffensive pushed German troops back. The Red Army absorbed the Wehrmacht's strongest blows and forced the unprepared Germans into a war of attrition. The Wehrmacht would never again mount a simultaneous offensive along the entire strategic Soviet–Axis front. The failure of the operation drove Hitler to demand further operations of increasingly limited scope inside the Soviet Union, such as Case Blue in 1942 and Operation Citadel in 1943 — all of which eventually failed. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: What is the main subject here?
Guess: Operation Barbarossa

Now answer the following question in the same format.

Question: When did it start?

In 1941