Although Mongol-led confederations sometimes exercised wide political power over their conquered territories, their strength declined rapidly after the Mongol dynasty in China was overthrown in 1368. The Manchus, a tribal group which conquered China in 1644 and formed the Qing dynasty, were able to bring Mongolia under Manchu control in 1691 as Outer Mongolia when the Khalkha Mongol nobles swore an oath of allegiance to the Manchu emperor. The Mongol rulers of Outer Mongolia enjoyed considerable autonomy under the Manchus, and all Chinese claims to Outer Mongolia following the establishment of the republic have rested on this oath. In 1727, Russia and Manchu China concluded the Treaty of Khiakta, delimiting the border between China and Mongolia that exists in large part today.