One could argue that World War I formally began on July 28, 1914, when Austria-Hungary declared war on Serbia. Throughout the previous month, the European continent had experienced ever-increasing tension owing to the assassination of the Austrian archduke Francis Ferdinand by Serbian nationalists on June 28. Within days of the Austrian move, Germany had declared war on Russia and France, England had declared war on Germany, and Austria had declared war on Russia. By 1915 two major alliances were locked in deadly embrace: the Allies (the major powers being England, France, Russia, and Italy) and the Central powers (the major powers being Germany, Austria-Hungary, and the Ottoman Empire). On August 19, 1914, President Woodrow Wilson called upon Americans to be “impartial in thought as well as in action,” by which he meant that, regardless of their sentiments, they should keep the interests of the United States primary in their thinking.