Final answer:
European nations formed alliances in the late 19th and early 20th centuries to prevent military conflicts and maintain peace, primarily due to rising political tensions and the arms race.
Step-by-step explanation:
In the late nineteenth and early twentieth centuries, European nations formed alliances primarily due to rising political tensions and the arms race. These alliances were a response to Germany's territorial ambitions and its desire to expand its colonial holdings, which threatened other imperialistic powers like Great Britain. The alliances were aimed at preventing military conflicts and maintaining peace in Europe.