The correct answer is Germany.
During World War I, Germany attempted to send the Zimmerman Telegram to Mexico. In this telegram, the Germans asked Mexico to invade the United States. The Germans asked of this because they knew if the United States was fighting with Mexico, they would not get involved in World War I. This would increase the chances of German success in this war.
The Zimmerman Telegram, however, was intercepted by allied forces and given to the American government. After reading this telegram, the American government declared war on Germany, essentially having the exact opposite outcome that the Germans were hoping for.