In 1914 Germany invades neutral Belgium in WWI leading to Britain’s declaration of War on Germany.
On the 28th of July 1914, after Serbia refused to accept all the ultimatums put forward by Austro-Hungary, the Austro-Hungarian government sent a telegram to Serbia declaring war. Russia had already promised to stand by Serbia and began to mobilize troops ready to defend their Serbian Allies. Germany had also promised to protect the interests of Austro-Hungary (they had even pushed Austro-Hungary towards war) and on the 31st of July Germany warned Russia to desist in its mobilization of troops. Russia attempted to assure Germany that its mobilization of its forces was for use against Austro Hungary only and not against any other nation of the Triple Alliance.
The Triple Alliance was formed when Austro-Hungarian Empire signed a treaty with Germany and Italy on the 20th of May 1882. It was a military alliance of the signatories which ensured support of the other nations in defence of aggression from any other “Great Power”. The Great Powers were Great Britain, France, Germany, Italy, Japan, Russia, Austro-Hungary, and the United States.
On the 17th of August 1892 France and Russia drafted their own Military Alliance in response, guaranteeing the others assistance if either was attacked by another Great Power. The Franco-Russian Treaty was completed on the 4th of January 1894. Great Britain had remained neutral but on the 8th of April 1904 they signed the “Entente Cordiale” with France which was a similar military alliance treaty on the 31st of August 1907 The United Kingdom and Russia signed a Military Alliance. These treaties between Britain, France and Russia became known as the Triple Entente and along with the Triple Alliance two great power structures had formed in Europe.
After the Assassination of Archduke Ferdinand it became obvious that the situation between Austro-Hungary and Serbia could have a massive knock-on affect with the other member nations of the military alliances with catastrophic war in Europe. Most of the powers of Europe were intent on finding a diplomatic way out of the situation including initially Austro-Hungary. Despite Russia’s assurance that they had no ill-intent against Germany, in the hope of preventing such a war, on the 1st of August Germany declared war on Russia. Italy, the other member of the Triple Alliance, declared its neutrality on the 2nd of August based on the principle that the military alliance was based on support for defensive purposes only, yet Austro-Hungary was actually the aggressor. Although this was the case Italy had also signed a secret alliance with France and would later enter WW1 on the side of the Allies (UK, France, Russia etc).
After declaring war on Russia Germany knew that war with France was imminent. In 1905 German Count Schlieffen had already formulated a plan to invade France which involved the Germany Army marching through the poorly defended “Low Countries” such as Luxemburg and Belgium rather than through Frances better defended boarders. On the 2nd of August Germany began its invasion of Luxemburg, claiming it was to gain access to France, however German forces continued their occupation of Luxemburg until its liberation at the end of the war and even disbanded the Luxemburg government.
On the 3rd of August Germany declared War on France. Germany had also sent an ultimatum to the Belgium Government on the 1st of August demanding they allow German troops access to France through Belgium. Belgium had already confirmed their neutrality leading up to the conflict and after receiving the ultimatum, Great Britain promised military support to Belgium in the event of an invasion. When the Belgium government refused the German army began the invasion of Belgium on the 4th of August and the Government of Great Britain sent a declaration of War to Germany. On the 5th of August the first battle of World War I began with the Battle of Leige. Germany planned to use the main railway line from Germany via Brussels and down to Paris running right through the City of Leige. This made the city of Leige very important in terms of a military invasion and as such many forts had been built their. The forts were self sustaining, with their own water and electric supplies as well as having sophisticated armour and weaponry. They were able to hold out against the mighty German army until the 17th of August when the Belgian Government was forced to leave the capital city of Brussels. Belgium remained under German occupation until 1918.