Answer:
D-Day was the day the allied powers landed and established a foothold in mainland Europe.
Step-by-step explanation:
Since 1940, when France surrendered and the British Expeditionary Force escaped Dunkirk, Axis aligned countries had control over western Europe. After D-Day, Allied forces (mainly English, American, and Canadian soldiers) gained a foothold in Northern France, which would be used to retake France, Belgium, and the Netherlands by 1945.