57. which of the following was not an act of military aggression that hitler undertook in the 1930s? hitler invaded belgium, the netherlands, luxembourg, and then france. hitler moved troops into the rhineland. hitler invaded poland. hitler threatened to invade czechoslovakia.

Hitler invaded Belgium, the Netherlands, Luxembourg, and then France

Explanation:

Germany and France had lot of tensions between them, and there were numerous battles between them, but nothing serious happened during the 1930's. In 1940 though, Hitler decided that it is the right time to invade quickly the Benelux countries that were neutral and strike France through them. the reason why Hitler went for these three small countries first was that they were very easy to invade, and also France had very weak defenses on the border with Belgium. Hitler's plan worked well, managed to invade these three small nations, and than attacked France where it was weakest, little by little taking over its territory.

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answer; biological;