Why did european nations from alliances in the early 1900s ?

Question

Why did European nations from alliances in the early 1900s ?

The main reason why European nations formed alliances in the early 1900s was that "They were unsure they could protect themselves if attacked by larger nations," since nationalism had caused nations to develop an "us vs. them mentality".

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necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.