In 1915, at a time when Romania kept its neutrality, the PSDR, led by the revolutionary-minded Marxist Christian Rakovsky, played a prominent part inside the anti-war Zimmerwald Movement. Throughout the following year, it organized rallies in support of non-intervention into what it deemed "an imperialist conflict". When Romania joined the Entente Powers in August 1916, the group came under suspicion of supporting the Central Powers, and was outlawed soon after. While its secretary Dumitru Marinescu was drafted and killed in action during the Romanian Campaign, several of its prominent activists, including Rakovsky, were arrested. Gheorghe Cristescu, Alecu Constantinescu, and others remained active in Bucharest under occupation by the Central Powers, and maintained links with the Social Democratic Party of Germany; the group, also including Ecaterina Arbore, Constantin Popovici, Ilie Moscovici, Ghiță Moscu, and Constantin Titel Petrescu, protested the peace with the Central powers and was arrested by the Alexandru Marghiloman government, but released through an amnesty soon after.