World War II

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World War II was a global conflagration involving dozens of countries, hundreds of battles, 100 million military personnel, and at least 70 million fatalities, an astonishing 50 million of whom were civilians. Its causes are still debated and the forces that propelled it are varied and complex. It was one of the defining events of the 20th century, affecting virtually everyone alive at that time and leaving an aftermath of international relationships many of which persist to this day. Any model that we create to interpret this eruption of human history will necessarily be a drastic oversimplification.

We make our model as simple as possible, including only five entities — the U.S., the British Empire, the Soviet Union, Germany, and Japan — and trying to interpret their interactions in light of quantitative realism. While obviously many other countries were involved, these five were the among most powerful and exercised the greatest agency in determining the course of events. We assume that relationships are always reciprocal, leaving only 10 to keep track of. We omit the geographic realities and the various theaters of operations, focusing instead on the belligerents' relative power levels, alliance structure, and periods of hostility.

To estimate the strength of the parties, we use the Composite Index of National Capability (CINC) as calculated by the Correlates of War Project. To estimate destructive power, we use data from the Correlates of War Project's database of Militarized Interstate Disputes. These disputes are coded via the hihosta variable using the numbers 1-5, with 5 representing war and 4 representing a variety of aggressive and destructive actions (MID 5.0 Codebook). We use values of 4 and 5, as explained further below, but not 1-3. This data set indicates the start and end date of the various hostility levels.

  • Data for cooperation
  • Parameters used

Sequence of Events

Setting aside for the moment the effect of cooperation and considering only destructive transfers of power, the following timeline summarizes the key events of the war:

Date Caption Relationships changed Event
5/10/1940 May 1940 {GMY,UKG} → -1 Beginning of the Battle of France
6/22/1941 June 1941 {GMY,RUS} → -1 Germany attacks Russia
12/7/1941 Dec. 7, 1941 {JPN,USA} → -1, {JPN,UKG} → -1 Japan attacks UK and US
12/11/1941 Dec. 11, 1941 {GMY,USA} → -1 Germany declares war on US
5/7/1945 May 1945 {GMY,UKG} → 0, {GMY,RUS} → 0, {GMY,USA} → 0 Germany surrenders
8/8/1945 Aug. 8, 1945 {RUS,JPN} → -1 Soviet-Japanese War
8/15/1945 Aug. 15, 1945 {JPN,USA} → 0, {JPN,UKG} → 0 Japan surrenders
9/15/1945 Sept. 1945 {RUS,JPN} → 0 Division of Korea

We can visualize this as a move sequence, with the countries placed in a circular arrangement rather than geographically:

WW2 sequence of events.png

The Law of Motion

Key Decision Points

Appeasement vs Resistance of German Aggression

German Prioritization of UK vs Soviets

  • Germany underestimated Russian military and economic strength, for example, expecting 200 Russian divisions and then encountering over 360 (Shirer pp. 1021-22).

Soviet Alliance with Germany vs the U.S. and UK

In August 1939, The Soviet Union signed a nonaggression pact with Germany. As Shirer 1959 notes (p. 656-7):

[T]here might not have been any war at all if Hitler had known he must take on Russia as well as Poland, England and France. Even the politically timid Germany generals, if one can judge from their later testimony at Nuremberg, might have put their foot down against embarking on a war against such a formidable coalition.

We have omitted Poland and France from our calculations, but let's consider what would have happened if the Soviets had instead made a pact with the British to counter German aggression together:


Timing of Japanese Provocation of U.S. and UK

  • Hitler underestimated the strength of the U.S. and overestimated that of Japan (Shirer p. 1069).

U.S. Prioritization of Japan vs Germany

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