December 7
US Congress Declares War on Austria-Hungary
On December 7, 1917, Congress passed a resolution declaring war on Austria-Hungary with only one dissenting vote, completing the United States’ formal entry into World War I against the Central Powers.
Summary
By December 1917, the United States had entered World War I against Germany earlier that year and faced pressure to address the full scope of the Central Powers alliance. On December 7, 1917, Congress approved a resolution declaring war on Austria-Hungary with only one dissenting vote. The declaration aligned US forces more completely with the Allied powers fighting on the Western Front and in other theaters. It came amid ongoing submarine warfare and diplomatic strains that had already drawn America into the conflict. American troops and resources subsequently contributed to operations against Austro-Hungarian forces until the empire's collapse in 1918.
Context
By the autumn of 1917 the United States had been at war with Germany for eight months. President Woodrow Wilson had asked Congress for that earlier declaration after German submarines resumed unrestricted attacks on American shipping and other neutral vessels. Austria-Hungary, Germany’s principal ally in the Dual Alliance, had broken diplomatic relations with Washington in April but had not yet been named an enemy. American planners grew concerned that Austro-Hungarian forces, fresh from successes on the Italian front, might require direct U.S. military attention if Italy’s defenses collapsed.
What Happened
On December 4 Wilson appeared before a joint session of Congress and delivered his annual message. He described Austria-Hungary as “the vassal of the German government” and urged lawmakers to remove “all impediments to success” by declaring war. Virginia representative Henry D. Flood promptly introduced House Joint Resolution 169. The House Foreign Affairs Committee endorsed the measure the next day, citing alleged acts of sabotage and submarine attacks attributed to Austrian forces. On December 7 the House adopted the resolution by a vote of 365 to 1; Socialist representative Meyer London of New York cast the sole negative vote. The Senate followed hours later with a unanimous 74–0 tally. Wilson signed the measure into law the same afternoon.
Aftermath
The declaration placed every major Central Powers government on a formal war footing with the United States and removed legal barriers to American operations against Austro-Hungarian units. U.S. troops and supplies already flowing to France could now be employed, if needed, on the Italian front or in other theaters where Habsburg forces operated. Within a year internal political disintegration and military reverses forced the Austro-Hungarian Empire into an armistice.
Legacy
The 1917 declaration formed part of the legal foundation for the postwar settlement that dismantled the Habsburg monarchy and redrew the map of Central Europe. Separate peace treaties between the United States and the successor states of Austria and Hungary were not ratified until 1921. Historians view the measure as a modest but necessary administrative step that aligned American policy fully with the Allied coalition and underscored the expanding global responsibilities of the United States.
Why It Matters
The declaration completed America's formal entry into the European theater of World War I and strengthened coordination with Britain and France. It supported the eventual dissolution of the Austro-Hungarian Empire and the redrawing of European borders after the war. The move underscored the expanding role of the United States as a global power.
Related Questions
Why did the United States declare war on Austria-Hungary months after declaring war on Germany?
Wilson initially postponed action because Austria-Hungary had not directly attacked U.S. shipping to the same extent as Germany; by December he viewed the declaration as necessary to remove legal obstacles and to address the deteriorating situation on the Italian front.
Who cast the only vote against the declaration in Congress?
Representative Meyer London, a Socialist from New York, was the sole dissenter in the House.
How did the declaration affect U.S. military operations?
It removed statutory barriers that had prevented American forces from engaging Austro-Hungarian troops, allowing fuller coordination with Allied commands in Europe.
What happened to the Austro-Hungarian Empire after the U.S. declaration?
The empire faced mounting internal strains and military defeats, leading to its collapse and the signing of an armistice in November 1918.
When was the state of war between the United States and Austria-Hungary formally ended?
Separate peace treaties with the successor states of Austria and Hungary were concluded in 1921.
Related Portfolio Site
US Military Atlas: US Congress Declares War on Austria-Hungary connects to military history, war consequences, or postwar diplomacy.
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Sources
- December 7, Wikipedia. Accessed 2026-07-07.
- On This Day - December 7, Encyclopædia Britannica. Accessed 2026-07-07.