On October 26, 1917, Brazil declares its decision to enter the First World War on the side of the Allied powers.
As a major player in the Atlantic trading market, Brazil—an immense country occupying nearly one-half of the entire South American continent—had been increasingly threatened by Germany’s policy of unrestricted submarine warfare over the course of the first two years of World War I. In February 1917, when Germany resumed that policy after temporarily suspending it due to pressure from neutral nations such as the United States, President Woodrow Wilson responded by immediately breaking diplomatic relations with Germany; the U.S. formally entered the war alongside the Allied powers on April 6, 1917.
One day before the U.S. declaration of war, a German U-boat sank the Brazilian merchant ship Parana as it sailed off the coast of France. On June 4, Dominico da Gama, the Brazilian ambassador to the U.S., wrote to Secretary of State Robert Lansing declaring that Brazil was revoking its previous neutrality and severing its own diplomatic relations with Germany. "Brazil ever was and is now free from warlike ambitions," da Gama stated, "and, while it always refrained from showing any partiality in the European conflict, it could no longer stand unconcerned when the struggle involved the United States, actuated by no interest whatever but solely for the sake of international judicial order, and when Germany included us and the other neutral powers in the most violent acts of war."
Over the next few months, Brazil’s government actively sought to amend its constitution to enable it to declare war. This having been accomplished, the declaration was made on October 26, 1917. In an open letter sent to the Vatican but clearly intended to be read in countries around the world, the Brazilian foreign minister, Dr. Nilo Pecanha, justified his country’s decision to enter the epic struggle of World War I on the side of the Allies by pointing to Germany’s attacks on international trade and invoking the higher purpose of creating a more peaceful, democratic post-war world: "Through the sufferings and the disillusions to which the war has given rise a new and better world will be born, as it were, of liberty, and in this way a lasting peace may be established without political or economic restrictions, and all countries be allowed a place in the sun with equal rights and an interchange of ideas and values in merchandise on an ample basis of justice and equity."
Though Brazil’s actual contribution to the Allied war effort was limited to one medical unit and some airmen, its participation was rewarded with a seat at the post-war bargaining table. The fact that Brazil—according to the size of its population—had three official delegates at the Paris Peace Conference in 1919 angered Portugal, who had sent 60,000 soldiers to the Western Front and yet had only one delegate. Britain supported Portugal in the disagreement, while the U.S. backed Brazil; no change was made. This conflict illustrated how important it was considered for the nations of the world to have representation in Versailles, as it was there that the boundaries of the new, post-World War I world would be determined. On June 28, 1919, Brazil was one of 27 nations to sign the 200-page Versailles Treaty, alongside a number of other Latin American nations who had also declared their support for the Allies, including Bolivia, Cuba, Ecuador, Guatemala, Haiti, Honduras, Nicaragua, Panama, Peru and Uruguay.