Through his son, Prince Barbu also communicated his plans for establishing the "United Principalities" of Wallachia, Moldavia, and Southern Bessarabia, with perpetual neutrality and full independence, to guard the mouths of the Danube against Russian encroachment. These plans also provided for the election to the unified throne of a foreign prince, unconnected to the boyardom. Drouyn de Lhuys promised to uphold these principles at the subsequent Vienna Conference of 1855, but modified them crucially, endorsing instead Moldavia and Wallachia's annexation by Austria, in exchange for a Franco–Austrian alliance treaty; this project failed to materialize. Attending the Paris Peace Conference in 1856, the "Beizadea" resigned himself to the discovery that his father's mandate would not be renewed, and from that point on demanded that a foreign dynasty be placed on Wallachia's throne. The Știrbeis also began lobbying for the construction of a railway from Kronstadt to Oltenița. If built, it would have been Wallachia's first.