The German bombings of Guernica and Durango in Spain in 1937 during the Spanish Civil War of 1936-1939 and the Japanese aerial attacks on crowded Chinese cities during the Second Sino-Japanese War in 1937–38 attracted worldwide condemnation, prompting the League of Nations to pass a resolution that called for the protection of civilian populations against bombardment from the air. In response to the resolution passed by the League of Nations, a draft convention in Amsterdam of 1938 would have provided specific definitions of what constituted an "undefended" town, excessive civilian casualties and appropriate warning. This draft convention makes the standard of being undefended quite high – any military units or anti-aircraft within the radius qualifies a town as defended. This convention, like the 1923 draft, was not ratified - nor even close to ratification - when hostilities broke out in Europe in 1939. While the two conventions offer a guideline to what the belligerent powers were considering before the war, neither of these documents came to be legally binding.