Why was the system of alliances in Europe before the first world war a threat to peace

For what reason was the arrangement of unions in Europe before the First World War a risk to harmony? For what reason was dominion a danger to harmony? since it constantly included the military triumph of different nations. No, in the end the US began battling close by Britain.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).

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