In August 1916, Romania declared war on Austria-Hungary and the other Central Powers. The subsequent campaigns ended in massive defeats and an invasion of the Romanian Kingdom territory. The government relocated to Iași, militarily backed by the Russian Republic. In July 1917, Imbroane, Goga, Sever Bocu and other Romanian defectors from Austria-Hungary were sent by the Iași government on a mission to Russia herself. They carried out propaganda work among the Transylvanian and Bukovinian prisoners-of-war, drawing them into a Volunteer Corps—for this purpose, they set up in Kyiv the newspaper "România Mare". He was by then integrated into the Romanian Land Forces as a lieutenant. "Stavka" recognized Imbroane as a Romanian government envoy and assigned him to approach prisoners working in the coal mines of Bakhmut and Seleznyovsky. According to his colleague Voicu Nițescu, Imbroane was "one of the most industrious, dedicated, and competent" recruiters, but met difficulty dealing with the local soviets. The latter wanted the Romanians kept in place until replaced by other captives.