What was the Zimmermann telegram?

The Zimmerman Telegram, written by the German foreign minister Arthur Zimmerman, was a document that ultimately aggravated and provoked the American public to encourage the war.

It was an offer of German aid for a Mexican invasion of America as revenge for the Mexican-American War. The Zimmerman Telegram was a proposal that stated that if the United States entered the war against Germany, it would be prudent for Mexico to side with Germany. In return, Germany would give Mexico back their "lost provinces," which was the land that Mexico lost in the 1840s, largely including Texas. Germany thought it would keep America out of Europe's war. However, the telegram was intercepted by the British and given to President Woodrow Wilson. By doing this, Germany quickened the United States' entry into the war. A month later, the US declared war on Germany.

Before this document, Germany was hoping that they could deteriorate the Allied defenses before the Americans could intercede. It affected the outcome of the war because it compelled the United States to get involved much earlier than anticipated in war that Germany hoped to win before the United States could even get involved.

The Zimmerman Telegram not only expedited the United States' entry into the war, but virtually made it an inevitability.

It is a common misconception that the Zimmerman Telegraph caused the US to enter into WWI. In fact it was a combination of all the factors that lead up to the war including the sinking of the RMS Lusitania from unrestricted submarine warfare. Some historians speculate that it could have actually pleas from Britain that money and supplies were running out. This was important to the US because they had major political and economic ties to Britain.