Austria-Hungary in World War I
Britain declares war on Austria-Hungary
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Original prompt & settings (JSON) ↗Britain had already been at war with Germany for eight days. This was a separate declaration — and Britain served France's in the same diplomatic package.
12 August 1914: a second British declaration
On 12 August 1914, Foreign Secretary Sir Edward Grey sent Austria-Hungary's ambassador in London, Albert Mensdorff-Pouilly, an official letter declaring war. Britain had been at war with Germany since 4 August; the alliance groupings did not produce one universal state of war, so a separate declaration was needed.
The British notice said Austria-Hungary's rupture with France obliged His Majesty's Government to announce that a state of war existed between Britain and Austria-Hungary from midnight.
Britain conveys France's declaration too
France and Austria-Hungary had already broken off diplomatic relations, so Britain acted as intermediary and conveyed the French declaration to Mensdorff along with its own communication.
Grey sent the formal notice with a sorrowful private farewell letter to Mensdorff, asking him to come and shake hands.
Eight in the evening, midnight in law
Mensdorff noted that the communication arrived at 8 p.m. and that he telegraphed its contents to Vienna at 8:15 p.m.
The legal state of belligerency waited for midnight, at the 12–13 August boundary, and the London Gazette notice was published on 13 August. An Admiralty order to commence hostilities followed the declaration.
Sources
Researched 23 Aug 2026 3 sources 2 audit passes Date corrected
How this was checked
Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →
Date corrected. The research places this at 1914-08-12.
What the sources leave uncertain
- The declaration was delivered and dated August 12. The Austrian State Archives describes the state of war as taking effect at midnight on the August 12–13 boundary; the London Gazette notice was published on August 13.