With China engulfed in chaos following the collapse of the Qing dynasty in 1911, Mongolian nationalists seized the opportunity to declared Outer Mongolia independent, with the support of Russia. Russia also took advantage of China's weakness to annex Tuva, thereby creating the modern Mongolia–Russia border. In 1915 the Second Treaty of Kyakhta was signed, by which Russia acknowledged formal Chinese suzerainty over Mongolia, albeit with Russia maintaining significant influence, leaving the country in effect as a semi-autonomous condominium. Following the Russian Revolution in 1917 China invaded Mongolia in an attempt to re-assert full control, however they were ultimately repulsed by Mongol and Soviet Russian forces, with Mongolia declaring independence in 1921, which was not recognised by China until 1946. Although an independent Tuvan People's Republic was declared in 1921, this small country became fully annexed into the Soviet Union in 1944, whereupon the former Mongolia–Tuva border became a section of the Mongolia–Soviet border. The latter stayed stable for the rest of the Soviet Union's existence, and continued as the Mongolia–Russia border after the dissolution of the Soviet Union in 1991.