A new border treaty between Germany and Denmark gives northern Schleswig to Denmark. The Estonian Constituent Assembly adopts the first constitution of Estonia, which will come into effect on December 21 this year. Duluth lynchings: Three African American circus workers are sprung from jail, subjected to a kangaroo court and hanged by a white mob in Duluth, Minnesota, in the northern United States. Australian soprano Nellie Melba becomes history's first well-known performer to make a radio broadcast when she sings two arias as part of an experimental series of broadcasts from a studio at the Marconi Company's factory at Chelmsford in England. June 22 – Greek Summer Offensive: Greece attacks Turkish troops. June 29 – The Republic of China joins the League of Nations. July July 1 – Germany declares its neutrality in the war between Poland and Soviet Russia. July 2 – Polish–Soviet War: The Red Army continues its offensive into Poland. July 7 – Arthur Meighen becomes Canada's ninth prime minister. July 11 – The East Prussian plebiscite is held. July 12 – Soviet–Lithuanian Peace Treaty: The Russian Soviet Federative Socialist Republic recognizes independent Lithuania. July 19–August 7 – The Second Congress of the Communist International takes place in Saint Petersburg and Moscow; the Twenty-one Conditions are adopted. July 20 – The United Kingdom cedes its brief control of the key Black Sea port of Batum to the Democratic Republic of Georgia. July 21 – The Interallied Mission to Poland takes place. July 22 – Polish–Soviet War: Poland sues for peace with Soviet Russia (which refuses). July 24 – Battle of Maysalun: The French defeat the Syrian army, whose leader Yusuf al-'Azma is killed. French troops occupy Damascus and depose Faisal I of Syria as king. July 26 – Mexican Revolution: Pancho Villa takes over Sabina and contacts Mexican President de la Huerta to offer his conditional surrender, which he signs on July 28. July 29 – The United States Bureau of Reclamation begins construction of the Link River Dam, as part of the Klamath Reclamation Project. July 30–August 8 – The 1st World Scout Jamboree is held at Olympia, London. July 31 Irish-born Australian Catholic Archbishop Daniel Mannix is detained on board ship by British authorities off Queenstown and prevented from landing in Ireland or from speaking in the main Irish Catholic communities elsewhere in the United Kingdom. France prohibits the sale or prescription of contraceptives. Representatives