This style of Kamja Salad, which uses a mayonnaise-based sauce, is not native to Korea at all. This style of potato salad originated in Northern Germany and was brought to the United States by German immigrants. Since most Americans are of German ancestry, (at least according to the US Census) this style of potato salad is quite common throughout the USA.
So far as I can tell, Koreans did not eat this style of potato salad prior to the Korean War. I believe it’s one of Koreas first “fusion” recipes before the idea “fusion cooking” became fashionable. It is a Korean adaptation of one of America’s most popular side dishes. —Tamar