Did Great Britain declare war on Germany in World War I?

In response to the assassination of Archduke Franz Ferdinand, Austria-Hungary declared war against the Serbians.  This occurred in July of 1914 and it was the beginning of World War I.  In August of that same year, the Germans invaded Belgium.  About seventy-five years before, Britain had entered into a treaty called the Treaty of London.  One condition of the treaty was that Britain would protect and defend Belgium in the event of invasion.  If Britain had not defended Belgium after the invasion by Germany, they would have been in violation of the Treaty of London.  In addition, the location of Belgium was close to Britain.  If the Germans ruled Belgium, they could easily attack Britain if they chose to.  The Germans hoped that Britain would not get involved, despite their invasion of Belgium.  The British, however, chose to honor the conditions of the Treaty of London.  They declared war on Germany on August 4th, 1914.