INCHEON, South Korea — Until recently, Beyond Cosmetics could not fill Chinese orders fast enough for its Green Piggy Collagen Jella Pack, a creamy beige substance containing pig collagen, or its Carbonated Bubble Clay Mask, which leaves the user’s face covered with foam.

Then, in November, international politics struck this South Korean maker of skin care products. As China’s ire grew over plans by Washington and Seoul to park a missile defense system on South Korean soil, sales of the two beauty aids fell to one-fifth of Beyond Cosmetics’ sales, from one-half.

Now, as the deployment of the system begins this week and China threatens to punish South Korea further, companies like Beyond Cosmetics have been bracing for worse. The intensifying diplomatic ruckus is exposing deep cracks in South Korea’s economic success story and forcing the nation to confront its dependence on China, its largest trading partner.

Even before the current crisis, Beyond Cosmetics had started to look beyond China, where it was increasingly running into problems like tougher government rules and rising homegrown competition.