King Albert I (Civ6)/Civilopedia

The nation of Belgium had been created at the end of the Napoleonic Era as part of the balance of European powers but had long been a special ally of Great Britain. The invasion plan of France called for the German Army to invade through Belgium. Indeed, early versions of the plan posited the Belgian Army would provide an honor guard along the roads for the passing German Army—a highly incorrect assumption, as it turned out.
The city of Liege was surrounded by a series of forts and represented the first significant military obstacle to the German Army in 1914. The forts, although they fought well in many cases, were unable to hold out against special siege guns constructed specifically for the purposes of breaking these forts. The collapse of the Liege fortifications and the cruelty of the German army against the population of Belgium turned the tide of popular opinion against Germany, especially in Great Britain.