The Mongolian River is a major river system in East Asia. It is composed of three rivers: the Amur, which is 4 letters long and forms the border between Russia and China; the IRO, which is 3 letters long and flows through Mongolia and China; and the LIAO, which is 4 letters long and flows through China and North Korea. Together, these three rivers form the Mongolian River, which is an important source of water for the region.