In august 1914 the germans invaded Belgium, expecting it to just let them through, this didn't happen and the country decided to fight, complicating matters is that the month of august had unseasonable heavy rain that struck hard and turned much of the roads and country side to mud and slowed the german advance to a crawl.
Thanks to a mixture of bad weather, and other lucky breaks the Belgians were able to successfully stop the germans at the city of brussels until the French and british empires could reinforce them. The country would then be split in two for the rest of the war. Everything to the east of the Brussle line was held by germany everything to the west of it to the allies.
The horrific stalemate would continue until 1918.
But what if the weather had been better and the Belgians less lucky, how would the war be changed if the german advance through Belgium had not been stopped? How would the world be changed?