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the alliance systems are one of the main causes that the war spread to so many countries. the war was originally between Austria-Hungary and Serbia. But, Russia was allied with Serbia so they began mobilizing for war. Germany was allied with Austria-Hungary so they declared war on Russia. Germany later declared war on France. To get to France, Germany went through Belgium. Belgium was allied with Britain so Britain declared war on Germany.

this continued until many more countries became involved.

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15y ago

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