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The most direct way nationalism caused World War I was through the assassination of Archduke Franz Ferdinand, who was the heir to the throne of the Austro-Hungarian Empire. ... Thus, nationalist movements broke out across the Slavic territories. Among the most militant nationalists were the Serbs.
Trench warfare is a type of land warfare using occupied fighting lines largely comprising military trenches, in which troops are well-protected from the enemy's small arms fire and are substantially sheltered from artillery.
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d. Dictatorship I think don't blame if it is wrong