Decisions made by the J.C. Deagan mallet instrument company at 1770 W. Berteau in Chicago are the sole reasons why A=440. I once worked in this building, still called the Deagan building.
The company made chimes and xylophones and instruments. They had customers all over the US. Each symphony in each city used a slightly different reference tuning. Philadelphia used 442, New York 438, etc.
This fact forced Deagan to retool their machinery every time a different order came in. This cut into profits. The owner, J.C. Deagan urged his customers to standardize on one reference tuning. One reference tuning meant one set of machine tools for his machines and no time or money spent retooling.
Deagan got results only when he contacted James Petrillo, the President of the AFM - the national musicians' union. Petrillo made it a work rule that A=440, overriding the conductors local preferences.
This was in 1910. Therefore there are no nazis involved.
http://richsamuels.com/nbcmm/deagan/index.html
Hey internet: don't be so goddamn gullible all the time, okay?