The paper comprises the first overview of profound and many-sided impact of World War I on socioeconomic life of Karelia. Based on archive materials and published sources the paper shows the growing geopolitical significance of the region in 1914–1918. The Olonets province and Kemsky district of the Arkhangelsk province became an important link in the communication system connecting the Russian Empire through the North European ports with the allied states. Geostrategic significance of Karelia was determined by the construction of the Murmansk railway, which joined the capital of Russia and the harbors on the Murman coast. Petrozavodsk as the centre of the Olonets province had at its disposal the Alexandrovsky cannon casting factory – a relatively big and well-equipped enterprise of the military and industrial complex of Russia. The comparative analysis indicates that during World War I the factory worked at its maximum capacity. The paper throws light upon some unrealized economic projects dealing with the wartime needs, yet relevant in the soviet period of Karelian history as a basis for the future development of industrial infrastructure of the republic. The study of the impact of military factor on the living conditions of the population of Karelia demonstrates particularly severe food crisis in the region compared to the Russian average, due to the poorly developed agrarian sector and great influx of migrants for the construction of the Murmansk railway. Still, despite a gradual fall of living conditions among various population strata during the war and an increase of social tension, the situation in Karelia was changing slower than in the centre of the state and was less politically determined.