One of China's biggest ever foreign policy successes will take concrete shape on Monday when delegates from 57 countries sign an agreement on the Asian Infrastructure Investment Bank (AIIB) in Beijing, Reuters reported. The founding members of the China-backed AIIB will sign articles of agreement that decide each member's share and the bank's initial capital. The multilateral institution, seen as a rival to the Western-dominated World Bank and Asian Development Bank, was initially opposed by the United States but has attracted many prominent U.S. allies including Britain, Germany, Australia and South Korea. Other founding members include most Asian nations and countries from the Middle East and South America. Japan and the United States are the most prominent nations not represented in the bank. China has said it has left the door open for them to join. "It's a huge diplomatic and strategic win for China," said Malcolm Cook, a senior fellow at the Institute of Southeast Asian Studies in Singapore, said of the AIIB.