His most notable work, and the beginning of his actions in the peace movement, was a 1876 book named Internationalism.[1]: 49 In 1878, he travelled to half-a-dozen Central European capitals to argue for organised peace.[1]: 49
De Marcoartu was a follower of Richard Cobden's free trade beliefs, attending meetings of the Cobden Club in London.[2] In 1889, de Marcoartu sponsored an essay competition on the "burdens of production" caused by the high taxation of militarism, with a winning prize of £150.[3] Accepting Spanish, French, and English entries, the judges for the French submissions were Léon Say, Frédéric Passy, and Jules Simon.[3] As the head of the Spanish Engineering Corps, he was involved in transferring Latin American concessions to the United States.[4]
