HO scale trains first appeared in the United Kingdom in the 1930s, originally as an alternative OO scale. It proved unsuitable for scale modeling UK trains. However, it became very popular in the United States, where it took off in the late 1950s after interest in model railroads as toys began to decline and more emphasis began to be placed on realism in response to hobbyist demand. While HO scale is by nature more delicate than O scale, its smaller size allows modelers to fit more details and more scale miles into a comparable area.