The article analyzes the first inter-state agreement at the end of the Russo-Turkish War of 1877–1878 – the so- called “Foundations of Peace”. It was signed on 19 / 31.01.1878. It provides the independence of Montenegro, Serbia and Romania, the autonomy of Bosnia and Herzegovina and the establishment of the Bulgarian Principality on the principle of ethnic majority with borders which can by no means be less than those defined at the Constantinople Conference of the Great Powers in 1876.