Germany’s invasion of which country started World War II

Poland

Explanation:

For several years before the Second World War, Germany showed aspirations to many territories, for which it considered that it was unfairly seized by the Versailles Treaty. In addition, the Germans considered themselves members of a higher race and that they needed a "living space" on which they had historical rights. One of the countries in which they especially had aspirations was Poland. Due to the lukewarm attitude of the Allies before the German demands, Hitler felt free to attack Poland without hesitation. Thus, on September 1, 1939, the Second World War began by the attack on Poland.

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