The Belgian civil war started in 1938 with the Flanders rebellion of November until January when the French declared Belgium annexed.
On 10th November 1939 Flemish insurrectionist supported by German intelligence services launched a rebellion in Flanders, while the Flemish rose up and took early success a quick counter attack by Walloon troops stemmed the rebellion.
This sparked a civil war between the government and secessionists. The Walloon government focuses it's efforts on keeping Brussels under control and they would move from there. While the Flemish rebels outnumbered the Walloon troops all the Walloon troops were armed with good equipment compared to sparsely armed Flemish rebels. In Brussels barracks the Flemish besieged the barracks for 18 days before it was relieved by Walloon troops.
As the street fighting in Brussels raged throughout the winter in diplomacy there was also a battle. The Germans had been about to move troops in but the French said they would declare war on Germany starting a world war. This caused the Germans to back down.
On 6th January at Leon Degrelle's request Charles Maurras ordered his army to mobilize and proceed to annex Belgium. Germany issued an ultimatum demanding that France demobilize and not intervene in Belgium. The French shortly followed by the rest of the Axis powers removed their ambassadors from the Allied powers and so the Allied powers removed theirs from the Axis powers. On the 8th January as the French ignore the German ultimatium the Germans declare war on France and World War II (Loyal Italy) starts.