During the Korean War, the North American F-86 Sabre helped the United States keep control of the skies. As aviation historian Joe Baugher notes, the Sabre shot down at least 792 MiG-15s during the conflict (another 118 were scored as "probable" kills). MiGs, on the other hand, had only 78 kills against the Sabre.
That's about a 10.15-to-1 ratio. If you include the probable kills, that ratio climbs to 11.67-to-1. That's a pretty decisive edge for the Sabre. So, why was the F-86 so dominant?
First, many American F-86 pilots were World War II vets. Among the better-known dual-war pilots were James Jabara (15 kills in Korea, 1.5 in World War II), Francis Gabreski (6 kills in Korea, 28.5 in World War II), and John W. Mitchell (11 kills in World War II, 4 in Korea. He also lead the mission that killed Isoroku Yamamoto). Pilot quality matters — just ask Japan.
Second, the F-86's armament was better for the air-superiority mission. The F-86 packed six M3 .50-caliber machine guns. These were faster-firing versions of the M2 machine guns used on the North American P-51 Mustang. By comparison, the MiG-15 had two NR-23 23mm cannon and one N-37 37mm cannon. This was designed to kill a lumbering bomber, not to deal with a fast, maneuvering fighter. Having the right tool for the job matters.
Third, the F-86 had a new, crucial piece of technology: the AN/APG-30, a radar gunsight. This made aiming the weapons much easier for the Sabre pilots. It used to be that a pilot (or anyone firing at an enemy plane) needed to judge angle and deflection on their own. With the AN/APG-30, the radar handled all that. All a pilot needed to do was to put the enemy plane in the center of his gunsight, squeeze the trigger, and bam, the MiG becomes a "good MiG." Making it easier to put lead on-target matters.
In short, the F-86 came in with three big advantages over the MiG-15. Those advantages helped the Sabre keep South Korea free from Communist domination.