In World War I, the so-called “Central Powers” of Germany and Austria-Hungary and the “Triple Entente” of France, Russia and Great Britain faced each other. Portugal joined the “Triple Entente” in 1916, and the United States joined the “Triple Entente” as an allied force in 1917.
The war was caused by the assassination of the Austro-Hungarian crown prince in Sarajevo in June 1914 and triggered a global conflict. The cause was the inability of the power blocs involved to achieve political balance. This situation was based in particular on excessive nationalism on all sides and the resulting personal demands. In addition, there was mutual distrust, which was further exacerbated by an arms race.
The conflict took place in three phases. The first, which lasted only a few weeks, was characterized by a rapid German offensive with major gains in territory in the west while simultaneously successfully repelling an attack by Tsarist troops in the east. This war of movement quickly degenerated into a war of position in which neither side was able to achieve a decisive victory. This phase lasted until the spring of 1918 and was accompanied by losses of soldiers killed, wounded and missing that had never been seen before.
In the naval warfare during the second phase of the war, with the increase in German submarine warfare, the Azores became increasingly important as a possible safe harbor and supply point on the Atlantic route, as the USA provided logistical support to Great Britain from the beginning, which was also a reason for Great Britain’s efforts to persuade Portugal to enter the war.
After the USA entered the war and with the introduction of armoured vehicles, the so-called “tanks”, on the Allied side, the economic and military balance of power finally tipped in favour of the Allies, and the German spring offensive of 1918, which was also directed against the Portuguese army in the Battle of La Lys on the battlefields of Flanders, did not change this.
The final phase of the war ended on November 11, 1918 with the signing of an armistice, followed by the conclusion of the Treaty of Versailles on June 28, 1919.