What if, the Romanian War Scare, combined with the annexation the Memelland, puts Chamberlain and France on edge. German movements near the French border set off an alert and on March 23rd, when Hungary invades Slovakia, French and German soldiers have a firing incident and things roll out of control from there. The next day, France declares war on Germany, and the British respond in kind, wary since the Dutch War Scare. The Germans, figuring if they wait any longer, they will lose the advantage, invade neutral Netherlands, in order to gain bases for air attacks on Britain, running down through into Belgium, in an attempt to invade France. Poland and Romania join the war on the side of the French and British.
How do things go from there? The Hungarians are technically invading a German ally, but if the Germans give Slovakia to the Hungarians, they can possibly gain another ally. Also, do the Italians join in? How do the Soviets respond?