Why do countries ally themselves militarily with others

Many countries ally themselves militarily with others to facilitate world peace. Otto von Bismarck of Germany founded this proponent. Bismarck believed that the European nations could ally in various ways in order to maintain a peaceful balance of power. The alliances emerged were quickly stable onward resulting to  unification and expansion of Germany that took place throughout early 1870.

the virginia plan called for three branches of government and two houses of congress. representation in each house would be determined by population. the new jersey plan called for three branches of government and a single house of congress. each state would have an equal vote.