Poland re-established its sovereignty in 1918 after a century of rule by Austria-Hungary, the German, and the Russian Empires; however, Poland's western and eastern borders were not determined at inception. The Soviet, Polish and Ukrainian claims over the disputed territories led to the Polish–Ukrainian and Polish–Soviet wars. The end of open warfare was achieved with the logistical aid by France. A formal treaty, the Peace of Riga, was signed on 18 March 1921, establishing Polish borders for the period between the World Wars. A process of economic recovery followed.