France has a better railway network connecting the center with the north.
WW1 begins as OTL, but the French launch the first attack through southern Belgium and the Germans are caught slightly off balance, fighting around Liege, but are slowly pushed back and have to fight both the Russians and French, with the latter being the more dangerous of the two.
Britain is annoyed at Belgian neutrality being broken and that the French/Russians appear to be winning, France makes territorial demands including large parts of the Rhineland because it believes it may win.
The Netherlands and Ottomans join in on the German side by mid-1915, then the British do to support their interests.