Perhaps because PONI starts in 1850 the 1838 London Treaty that gaurented Belgian independance should automaticaly come into play if any of the signatory nations invade Belgium?
This being the treaty that Bismarck scruplusly observed during the Franco-Prussian War with the pay of of British neutrality but which Wilhelm II dismissed as 'The scrap of paper' thereby gaureneeing that in 1914 Britain would fight to preserve Belgian independance.