Participation in the European War that began in 1914 offered Portugal's Republican leadership a unique opportunity to consolidate the regime that it had unveiled in October 1910. The support of the whole nation might be harnessed if a propaganda campaign managed to demonstrate clearly the need for unity in the face of a common and mortal danger; if, in other words, the Portuguese were led by the government to overcome their political, religious and economic differences in order to act as one, and thus emerge triumphant from the conflict (Teixeira 1996). Participation in the European conflict also offered up the possibility of demonstrating in a practical form, intelligible to all, the strength and virtue of the Republican creed: if all had to face the same wartime dangers, serving in the ranks of the army wherever it may be sent, and to endure the same sacrifices—rationing, military requisitions, taxes on war profits—then the virtues of equality, a mainstay of Republican political discourse, would be made clear to the whole country. In order to demand such sacrifices, the government would have to explain the reasons for Portugal's participation in the conflict, and this process would bring it closer to the 6 million Portuguese, the majority of whom lay, because of restrictions on the franchise, outside the realm of politics. Portugal might not be strong enough to tip the military balance in favour of the Western Allies, but the young Republic could benefit enormously from active participation, in so far as it would be able to rally the country's population for the first time in its 6-year life, thereby neutralising the influence of its enemies over the rural population. For this gamble to pay off, it was imperative that the war be seen by the Portuguese as a national conflict, and not one desired by the Republicans for partisan advantage: the primary task of war propaganda would be to make sure that the desired interpretation of the motives for Portugal's participation in the war became clear to all. The aim of this article is to describe the propaganda campaign carried out in 1916 and 1917, demonstrating its shortcomings, advancing some reasons for those shortcomings, and establishing the link between the failure of the campaign and the overthrow of the Republican government in December 1917...