In August-October 1914, Belgium was being invaded by the Germans. The German invasion began when the Belgian government issued a statement that they would uphold neutrality among the states that resided alongside them. However, in August 1914, Germany sent an ultimatum to Belgium that if they did not allow them to pass through in order to invade France, that they would invade Belgium as well. The deadline to respond to the ultimatum was two days, and Belgium did not respond. The British became aware of the German ultimatum and promised support and military support to Belgium.
After Belgium refused to accept the ultimatum, German invaded Luxembourg and the city of Liege. German were supposed to bring their infantry and invaded various cities of Belgium. From early to mid August, Germany invaded Belgium and since the Belgian government was undersupplied, their army fell to the Germans. Brussels, was then occupied and seized on August 21.
After various battles against Germany, most of their land was seized. The Belgian government only had various pieces of land before Germany took full control of Belgium. The army ended up creating a zone for communication among the other armies that the Belgian army aimed to thwart, but failed to do so. This led to mass German resistance and created high levels of tension among the Germans and Belgians. Ultimately, Belgium fell suspect to being hostages and got towns to be burnt down by the Germans which became infamously known as the Rape of Belgium.
After the Rape of Belgium, Germans continued to seize parts of Belgium and leaned their way towards France. Various parts of the armies stayed in Belgium to fight against the invasion, but failed to do their job. On August 27, 1942, the Navy for the British military tried to help combat the invasion, but failed to help. The plan was have the Royal Naval Air fly to Ostend and land on France and try to help aid the fight.
On October 2, 1942, the Marines that are a part of the Royal Military began to set up operations in the French and Belgian coast. Antwerp ended up being seized and their campaign failed due to the Germans, The Germans were highly equipped and were able to gun down the attempt of forts and blockades. A week later, on October 9, the British and Belgians surrendered to the German army.
During the campaign, which was known as the Race to the Sea, both opponents aimed to take the coast of Belgium and French to access the sea and be close to ports. The German intent was to take control of the coast and to take control of the area which would lead to decrease in supplies that the French and British would give to the Belgians. Also, the coast would allow easier access to France, which the Germans would plan on invading sooner or later.
With all these campaigns, Belgium ended up falling under German control by the end of November and would continue to be under their rule until the end of World War I, which was not until late 1918.