Three Emperor's League: This was a diplomatic alliance was between Germany, Austria-Hungary, and Russia planned by Otto van Bismarck in 1872. The aim of this alliance was to maintain the social order of the conservative powers in Europe and to keep peace between Austria - Hungary and Russia and to isolate Germany's enemy France. The alliance was broken slightly which was caused by the Russian- Turkish war which started in 1877 and ended in 1878. Russia and its ally Serbia came to help Bosnia and Herzegovina and Bulgaria in their fight against Turkish rule.
The Russians attacked through Bulgaria, and we able to successfully defeating Turkey were able to create the Treaty of San Stefano with Turkey in 1878. This treaty was able to free Romania, Serbia, and Montenegro from Turkish rule, and give independence to Bosnia and Herzegovina. However Germany, Austria - Hungary were alarmed by the huge gain in territory the Russian had won.
The Treaty of Berlin was later put in place to replace the Treaty of San Stefano by the European major powers. It's aim was to restrict the military and political gains made by Germany.
Dual Alliance: The Dual Alliance was between the countries Germany and Austria-Hungary. On October 7, 1879 a treaty was made, in it Germany and Austria-Hungary both agreed to aid one another if one of them would be attacked by Russia. Also, each state promised they would remain neutral to the other if one of them was attacked by another European power. In 1881 to 1887 the emperor's league was redone. There were secret negotiations between Russia and Bismarck concerning Germany's alliance with Russia. Germany would be neutral if Russia was attacked by Austria-Hungary.
Triple Alliance: This was a treaty by which Germany, Austria-Hungary, and Italy agreed to support each...