The origins of the conflict

Since 1904, date of the first clashes between the two major European blocks, Europe is in turmoil. On the one side, the Triple Alliance (Germany, Italy and Austria-Hungary), and on the other side the Triple Entente (France, Great Britain and Russia).

The slightest incident can trigger the disaster. The inevitable occurs on 28 June 1914. The Archduke Franz Ferdinand (nephew and heir of the Emperor of Austria) and his wife are murdered in Sarajevo, capital of Bosnia. The attack is carried out by Bosnian Serbs of the terrorist organisation «Black Hand».
 

 
Austria takes advantage of the pretext thus on hand, and, after an ultimatum rejected by Belgrade, declares war on Serbia on 28 July 1914. The inexorable cycle starts. Nothing can stop it.

Russia goes into action, Germany does the same, followed by France.

Then events start happening very quickly: on 1 August Germany declares war on Russia, on 2 August it demands free passage of its troops from Belgium, on 3 August it declares war on France and on 4 August it violates the Belgian neutrality. Great-Britain, at first in expectation, cannot remain insensitive to the crime and in turn declares war on Germany. It must keep its word and cannot consider the recognition of Belgian neutrality as «a scrap of paper».

A great disappointment, however, awaits Germany: Italy considers that the German aggression releases it from its allied obligations and proclaims its neutrality.

On 4 August 1914, the huge German war machine enters Belgium.