What was a shared reason why austria hungary and germany became members of the triple alliance

The agreement between Austria Hungary ,Italy and Germany  was called Triple Alliance. It was formed on 20th may 1882 and lasted till 1915. When Italy lost its north African Territories to french, it stated to look for support and joined Triple alliance with Austria-Hungary and Germany. The members of Alliance promised to support each other in case of attack by any of the great powers. The countries had agreed to support each other if France or Russia attacked any of the members. This alliance threatened France. Britain was also threatened by the growth of German navy. So both Britain and France formed Entente Cordiale to deal with the German threat.  Russia was also afraid of German Navy so it also joined France, Britain and formed Triple entente. The entente stated that the countries had a moral obligation to support its members.  

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