The tensions from European Imperialism did not only cause the entanglement of alliances, but lead to countries strengthening their military. ... In European nations like Germany, nationalism was driven by imperialism. Nations like Britain and Germany were expanding and thought they were unstoppable.
The other alliance was the Triple Entente. This included Soviet Union (Russia), Great Britain, and France. The danger of these alliances is that if a member from one alliance declared waron a member from the other alliance, the conflict would quickly escalate. That is what happened in World War I.