The Sixtus Letter: Emperor Charles' Failed Attempt at Peace in World War I

The Content of the Sixtus Letter
In his famous letter to Prince Sixtus on March 24, 1917, Emperor Charles declared his willingness "to support the just French claims regarding Alsace-Lorraine with all means and all influence at his disposal with his allies." In addition, Belgium was to be restored and compensated. Serbia was to regain its sovereignty and gain access to the Adriatic Sea.
With these concessions, the young emperor hoped to win France over to peace. His foreign minister, Count Czernin, was informed about the talks but did not know the exact wording of the letter. A second letter on May 9 reaffirmed the Austrian positions.

The Failure of the Peace Efforts
The conditions of the Entente conveyed by Sixtus would have amounted to a defeat. In particular, the strengthening of Serbia and Russia was unacceptable to the Danube Monarchy. France was also not willing to give the German Empire a free hand in the East in return.
When French Prime Minister Clemenceau published Charles' first letter in April 1918 to refute a statement by Czernin, the emperor denied further letters and concessions. Thus, he was exposed to the German ally. The affair meant the end of Austria-Hungary as an equal partner and definitively destroyed the prospects of a peace of understanding with the Western powers.