The early 20th century brought economic prosperity to the Netherlands, creating new opportunities for insurers. Life insurance companies expanded into Belgium through acquisitions, while modernising their organisations became a priority. De Nederlanden relocated its headquarters to The Hague and focused on creating an attractive workplace. Initiatives included trainings for talented colleagues, implementing a staff pension scheme, and offering holiday homes for lower-paid workers.

The global economic crisis of the 1930s led to mass unemployment and wage cuts. During this challenging period, insurers faced declining premium income. Nationale, recognising the hardships of low-income citizens, provided insurance to those hit hardest by the depression.

The Second World War had an enormous impact on the Netherlands and the Dutch people. Offices of both companies were bombed and destroyed and a total of 46 employees, including many Jewish colleagues, lost their lives during the war. The Nazis forced Jewish citizens to surrender their life insurance policies. After the war, delays in payments to Holocaust survivors further compounded the injustices. In 1999, NN, together with other Dutch insurance companies, helped set up a fund to rectify past wrongs and provide reparations to the Jewish community.