Prior to the establishment of formal diplomatic relations between the United States and the Soviet Union in 1933, American military intelligence on the Red Army was limited to what it could glean from foreign military sources and travelers who had observed the Red Army inside the Soviet state. Thus, from 1920, the end of the period of Russian Civil War and Allied Intervention, to 1933, information on the Soviet military establishment was gathered by American military attachés from European diplomatic and military officials in Riga, Berlin, and Warsaw. To a lesser extent, intelligence on the Red Army was also available in London, Paris, Vienna, Stockholm, Tokyo, and Peking. American military intelligence dispatches and reports during the period reflected the heavy reliance upon secondary and indirect sources, although the information was often remarkably accurate. But with the American diplomatic recognition of the Soviet Union and the opening of an American embassy in Moscow, American military intelligence gained the opportunity to supplement information received from foreign military sources with data received directly from the American military attaché.