The Schlieffen Plan specified passage through Belgium, a neutral country. Rather implausibly, Count von Schlieffen had contended that Belgian neutrality might be preserved if they simply allowed the German armies free passage. In the event, the Germans claimed that French officers had been secretly passing through Belgium to Germany, so their invasion was justified, a quid pro quo. When the invasion commenced, on 4 August, there were protests and examples of resistance, which the Germans magnified as a pretext for martial law. They committed brutal acts of suppression including massacres of unarmed civilians in Dinant and Leuven. The conquest was not uncontested; there was stout resistance at the sieges of Antwerp and Dixmude and, following the Battle of the Yser, the southwestern corner of Belgium remained free throughout the war. The invasion triggered Britain’s declaration of war by violating the 1839 Treaty of London.