In August 1914, the German Empire invaded neutral Belgium. The campaign was initially very successful, pushing the Belgian, French and British forces westwards. By the end of 1914, however, the Western Front had stabilised into static trench warfare. Following the Battle of the Yser in October, the Belgian army remained entrenched along the Yser Front and was left with a number of armoured cars which could not be used. In early 1915, the Russian Tsar Nicholas II formally requested military support from King Albert I and a self-contained unit was formed for service in Russia. As Belgium was officially an independent neutral power rather than an ally of the Russian Empire Belgian soldiers in this unit were officially considered as volunteers in the Imperial Russian Army itself.