After months of inaction, Germany launches an invasion of Denmark and Norway on 9 April 1940. The invasion in Norway was unopposed as commanders were sympathetic to former foreign minister and pro-fascist Vidkun Quisling. Once the troops were landed, Norway was ordered to surrender but decline. Germany sent in paratroopers and took control putting Quisling in charge of government. However loyal troops refused to surrender and fought with British troops against the Germans. The British troops, however, were ordered to France due to German troops advancing there. Norway was forced to surrender and with compliant government in place, the country was secured. Denmark, having not a military strong enough to repel the invasion, would capitulate.

The Danes negotiated a deal where full German occupation did not occur and was allowed to mostly remain somewhat independent. However by 1943, Danish resistance to the Germans had grown causing problems with sabotage. In response, the Germans demanded tighter controls but the government refused. Germany dissolved the government and took over running Denmark directly. Danish Jews were now at risk of being deported. When word was received of  an upcoming pogrom on Rosh Hashanah in October 1943, Jews were told to go into hiding by Danish people. Nearby Sweden offered a haven and was unoccupied by the Nazis. And it was close (3 miles away). Jews were ferried across in fishing boats and it was not exactly comfortable and often terrifying. However, 7,000 managed to flee to Sweden leaving only around 500 Jews who could not get away. Those Jews were sent to Theresienstadt. Of them only 51 perished and were saved by persistent support of the Danish for those being held at Theresienstadt. 90% of Danish Jews escaped the Holocaust thanks to righteous Danes.

Sources:

History.com
History Learning Site

Articles (Online)

How the Danes Saved the Jews, jmshistorycorner
Holocaust Rescue: Rescue of Danish Jews, Jewish Virtual Library