South Korea has a number of allies around the world who support its efforts to achieve peace on the Korean Peninsula and its economic development. The United States has been a key ally since the Korean War, while Japan is an important trading partner. China, one of South Korea's largest trading partners, has strained relations due to disagreements over missile defense systems and North Korea. Australia, the European Union, Russia, India, Singapore, New Zealand, Philippines and Thailand also have strong relationships with South Korea in terms of trade and shared concerns about North Korea's nuclear program.