Austria-Hungary at war with Portugal

On 15 March 1916 Portugal found itself at war with Austria-Hungary as well. The British chronology of the war records two events under that date: Vienna’s breaking off of diplomatic relations with Lisbon and an Austro-Hungarian declaration of war. Most later lists of the declarations of war of 1914–1918 give the same date.

Contemporary sources, however, describe the matter more cautiously. On 16 March the American minister in Lisbon, Thomas Birch, cabled Washington: “Diplomatic relations between Portugal and Austria-Hungary broken. No declaration of war.” The compendium “The People’s War Book”, published in the United States in 1919, lists among the declarations of war on Portugal only Germany’s step of 9 March, and counts Austria-Hungary’s decision among the severances of diplomatic relations, dated 16 March. The Portuguese government, too, in its official report of 1917, speaks only of the breaking off of relations with Austria. Everything therefore suggests that Vienna handed over no separate declaration of war, and that the state of war followed from the breach of relations at a time when its closest ally was already fighting Portugal. The British yearbook “Annual Register” wrote of it as a matter of course: Germany’s declaration of war “of course involved also war between Portugal and Austria-Hungary”.

Following the ally

Formally, Vienna did not have to follow Berlin. The Dual Alliance of 1879 was a defensive alliance, directed above all against Russia, and did not oblige Austria-Hungary to go to war with every enemy of Germany. Nor did war automatically extend to all members of a coalition. Italy had been fighting Austria-Hungary since May 1915, while for more than a year it formally remained at peace with Germany.

In practice, however, Austria-Hungary, increasingly dependent on Germany in 1916, could not maintain normal relations with a state with which its ally was at war. The dispute with Portugal also concerned Vienna directly. The Portuguese had requisitioned not only German ships but also two Austro-Hungarian ones, and the seizure of the ships in the Tagus was the immediate cause of Germany’s declaration of war.

A war without a front

The new state of war had little practical significance. Austria-Hungary and Portugal had no common border and no disputed territories. In the following years Portuguese soldiers fought the Germans in East Africa and in France, not the Austro-Hungarian army. The war with Vienna nevertheless gave Lisbon a place among the states that, after the defeat of the Central Powers, also made peace with Austria and Hungary. In 1919 Portugal signed the peace treaty with Austria at Saint-Germain-en-Laye, and in 1920 the treaty with Hungary at Trianon.