i like the ideas that come in, but there are some things i don't think seem realistic.
let's start with the revolution, i think there are three senario's where in a succesfull communist revolution is realistic.
1) The German communists also sense the time is right for a revolution and within days the rebellion storms the Reichstag. Unwilling to fight there own people the army sides with the Revolution and the German Socialist Republiek is proclaimed giving the Netherlands a strong ally. Perhaps a leftist revolt in France would happen (is nice, but it isn't really important).
2) Communists around Europe begin to make there move, following the Dutch example. However they don't get the swift take-over they hoped for in most cases. The German Revolution starts a terrible civil war witch takes over a year to supress. In France the workers take Paris and kill the Poincaré (the president) and some generals (here a French revolt is important). Troops who had recently been fighting foreigners where sent to murder there own people (I think the Great War ended practicly or a ceasefire was declared by both parties) and they deserted an masse, the British have to be shiped in (and brought in from the former western front)to crush the Revolution, leaving Frances honour shattered and more importantly there is a lot of civil unrest. The UK have had there share of the war. Putting down one rebellion is enough for the Brits, they leave the German civil war to the Germans (let's say the country is so divided that no side wins until 1922 leaving the lands broken and the economy destroyed) and why would they invade a country (even as small as the Netherlands) when the troops have fought four years of the bloodiest war in history only to shoot at former allies when it is over. About America we doen't have to worry either they went isonalist the minute the war ended. This leaves the door open for a possible annexasion of Flanders (perhaps even most wallone too).
3) Thanks to Wolfpaw for this idea. With the war over, the French deside they don't want a socialist state so close there home country and they invade (perhaps with British support or even American (I don't thinks so but it's an option)). What they think would be a quick invasion, done by the book, turns out to be a horrible small urban copy of the Great War. Leaving Dutch streets flooded with the blood of reactionary French troops. Here we have another option to gain (parts of) Flanders, if France attacks they will move over Belgium and the Belgium goverment also send troops to help the invasion in the hope of gaining Limburg or Zeeuws-Flanders or both. If Belgium supported the invasion why won't take the Dutch the fight to Belgium?