The common element in the response of Denmark, Sweden, and Norway to the outbreak of both world wars was a widespread desire to remain neutral. In the First World War, all of these attempts were successful. In the Second World War, two of the three attempts at neutrality failed. That is, while Sweden was able to remain neutral, both Denmark and Norway were invaded by the armed forces of National Socialist Germany and occupied for five years.

In the Second World War, the German occupation of both Denmark and Norway was opposed by local resistance movements. In Denmark, the great achievement of the resistance movement was the successful evacuation of about 7,000 Jews - nearly the entire Jewish population of Denmark - to Sweden. In Norway, the most notable single achievement of the resistance movement was the destruction of the heavy water facility at Telemark. At the same time, a number of people in both Denmark and Norway collaborated with the Germans, and thousands of citizens of both countries volunteered for service with the German armed forces.