The last Habsburg emperor was unexpectedly thrust into the role of heir to the throne after the assassination of his uncle Franz Ferdinand at Sarajevo. In the first years of the war he served as a staff officer, commanding the XX Corps in the Austrian Tyrol offensive of May 1916 and moving to Galicia that summer in the wake of the Brusilov offensive. Karl performed well in these engagements but remained inwardly skeptical about the chances for an ultimate Austro-German victory.
His Catholic and humanitarian sentiments would have a profound effect on policy after he became emperor on the death of Franz-Josef on November 21, 1916. Karl was convinced of the inhumanity of the war and was prepared from the beginning to seek a way out of it. He also feared the growth of German political and military influence in the alliance. His involvement in the Sixtus affair of the Spring of 1917 was therefore a matter of policy rather than a gesture of despair.
The initiative for peace talks through Prince Sixtus, Karl's brother-in-law, actually came from Poincare in France; but whereas Karl's sincerity in seeking peace is not in doubt, French officials were more interested in contributing to a rupture of the Austro-German alliance. Karl pledged in writing to support the restoration not only of Serbia and Belgium, but also of Alsace-Lorraine to France and the Trentino region to Italy. His concessions made little headway against French and especially Italian obstinacy, and when Clemenceau made public Karl's promises regarding Alsace-Lorraine in April 1918, the damage to the relations among the Central Powers was severe. The Emperor's attempts to reform the domestic political order in Austria-Hungary also foundered, partly because of Hungarian and Austrian vested interests and partly as a result of Karl's own weakness of will.
The October manifesto of 1918, in which Karl attempted to realize his dreams of a federalist reconstruction of his empire, came far too late to have any effect other than hastening the collapse of Austria-Hungary. He renounced political power on November 11 but refused to abdicate, moving into Swiss exile in March 1919. Unlike his German counterpart Wilhelm II, Karl refused to accept the end of his dynasty. His attempts of March and October 1921 to return to power in Hungary were, however, fiascos. He died in penury in Madiera, Portugal, in 1922. His refusal to accept the end of the Habsburg dynasty had been, like most of his actions, a matter of principle. Karl's personal moral integrity was unique in the era of Ludendorff and Lloyd George; and it is perhaps indicative of the times that he was ultimately such a failure as a king and politician.
Sources: Gordon Brook-Shepherd, The Last Habsburg. New York: Weybright & Talley, 1968.
Holger W. Herwig and Neil M. Heyman eds., Biographical Dictionary of World War I. London: Greenwood Press, 1982.