The MiG-15 made its entrance during the Korean War, flying over from China to challenge the undisputed United Nations air superiority over the area. It became such a thorn in the side of Allied forces that the B-29 Superfortresses were relegated to the more limited night flying bombing campaign. The United Nation forces were limited by a self-imposed rule that ensured they could not engage in targets outside of the designated Korean Peninsula theatre of war - the result of which was a greater complication and escalation of the war as a whole.