The International Sanitary Conferences (ISC), the first of which was held on 23 June 1851, were a series of conferences that took place until 1938.[12] The first conference, in Paris, was almost solely concerned with cholera, which would remain the disease of major concern for the ISC for most of the 19th century. With the etiology, even the communicability, of many epidemic diseases still uncertain and a matter of scientific argument, international agreement on appropriate measures was difficult to reach.[12] Seven of these international conferences, spanning 41 years, were convened before any resulted in a multi-state international agreement. The seventh conference, in Venice in 1892, finally resulted in a convention. It was concerned only with the sanitary control of shipping traversing the Suez Canal, and was an effort to guard against importation of cholera.[13]: 65  Five years later, in 1897, a convention concerning the bubonic plague was signed by sixteen of the 19 states attending the Venice conference. While Denmark, Sweden-Norway, and the USA did not sign this convention, it was unanimously agreed that the work of the prior conferences should be codified for implementation.[14] Subsequent conferences, from 1902 until the final one in 1938, widened the diseases of concern for the ISC, and included discussions of responses to yellow fever, brucellosis, leprosy, tuberculosis, and typhoid.[15] In part as a result of the successes of the Conferences, the Pan-American Sanitary Bureau (1902), and the Office International d'Hygiène Publique (1907) were soon founded. When the League of Nations was formed in 1920, they established the Health Organization of the League of Nations. After World War II, the United Nations absorbed all the other health organizations, to form the WHO