On 21 August 1944, the Battle of Normandy ended and the allied forces quickly advanced towards the North and East of France.
For instance, Brussels was liberated on 3 September, and the allied forces already reached Germany, notably Aachen on 16 September.

However, some pockets of German resistance remained along the coastlines and Calais, Boulogne, Dunkirk and Antwerp were still occupied. So as to prevent the allied forces from taking control of the ports, which were paramount to the war effort, major coastal towns and cities were granted the status of Fortress (Festung) by Hitler, and were particularly heavily guarded.

In September, failure of Operation Market Garden slowed down the allied progress, as well as liberation of coastal towns and cities.
A siege took place in Dunkirk on 15 September; Boulogne was captured on 17 September, Calais on 25 September, but it was necessary to wait until the Battle of Escaut before Antwerp was liberated, on 3 November, and Middelburg on 7 November. However, Dunkirk was still held by the Germans. During this battle, on 7 October, the town of Vlissingen suffered heavy bombing, which led to many civilian losses.

The German counter-offensive in the Ardennes halted the allied advance, and the Netherlands would not be fully liberated until several days before the end of the War and Dunkirk was only liberated on 9 May 1945, after signature of the German surrender.

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