Introduced in 1946 by Indonesian nationalists fighting for independence, the currency replaced a version of the Netherlands Indies gulden, which had been introduced during the Japanese occupation in World War II. In its early years, the rupiah was used in conjunction with other currencies, including a new version of the gulden introduced by the Dutch. The Riau islands and the Indonesian half of New Guinea ("Irian Barat") had their own variants of the rupiah in the past, but these were subsumed into the national rupiah in 1964 and 1971, respectively (see Riau rupiah and West Irian rupiah).