January 1 – The St. Petersburg–Tampa Airboat Line in the United States starts services between St. Petersburg and Tampa, Florida, becoming the first airline to provide scheduled regular commercial passenger services with heavier-than-air aircraft, with Tony Jannus (the first federally-licensed pilot) conveying passengers in a Benoist XIVflying boat. Abram C. Pheil, mayor of St. Petersburg, is the first airline passenger, and over 3,000 people witness the first departure.
April 4–September 27Komagata Maru incident: The Komagata Maru sails from India to Canada. Due to Canadian regulations designed to exclude Asian immigrants, the boat is not permitted to dock in Vancouver, and is forced to return to Calcutta with all its passengers.
April 9 – Tampico Affair: A misunderstanding involving United States Navy sailors in Mexico, and army troops loyal to Mexican dictator Victoriano Huerta, leads to a breakdown in diplomatic relations between the United States and Mexico.
April 14–18 – The first International Criminal Police Congress is held in Monaco; 24 countries are represented, including some from Asia, Europe, and the Americas; the Dean of the Paris Law School is president.
April 21 – United States occupation of Veracruz: 2,300 U.S. Navy sailors and Marines from the South Atlantic fleet land in the port city of Veracruz, Mexico, which they will occupy for over six months. The Ypiranga incident occurs when they attempt to enforce an arms embargo against Mexico, by preventing the German cargo steamer SS Ypiranga from unloading arms for the Mexican government in the port.
April 22 – Mexico ends diplomatic relations with the United States for the time being.
July 5 – A council is held at Potsdam, powerful leaders within Austria-Hungary and Germany meet to discuss the possibilities of war with Serbia, Russia, and France.
July 7 – Austria-Hungary convenes a Council of Ministers, including Ministers for Foreign Affairs and War, the Chief of the General Staff and Naval Commander-in-Chief; the Council lasts from 11:30 am until 6:15 pm.
German troops invade Belgium at 8:02 am (local time). Great Britain declares war on Germany, for this violation of Belgian neutrality. This effectively means a declaration of war by the whole British Empire against the German Empire, beginning World War I from the British perspective. The United States declares neutrality.
British colonial troops of the British Gold Coast Regiment, entering the German West African colony of Togoland, encounter the German-led police force at a factory in Nuatja, near Lomé, and the police open fire on the patrol.Alhaji Grunshi returns fire, the first soldier in British service to fire a shot in the war.
Lake Nyasa is the scene of a brief naval battle, when Captain Edmund Rhoades, commander of the British steamship SS Gwendolen, hears that war has broken out, and he receives orders from the British high command to "sink, burn, or destroy" the German Empire's only ship on the lake, the Hermann von Wissmann, commanded by a Captain Berndt. Rhoades's crew find the Hermann von Wissmann in a bay near "Sphinxhaven", in German East African territorial waters. Gwendolen disables the German vessel with a single cannon shot from a range of about 1,800 metres (2,000 yards). This very brief engagement is hailed by The Times in England, as the British Empire's first naval victory of World War I.