First of all, let's make a simple understanding of the organization of the European Union. As the name implies, the main members of the European Union are all European countries. The reason why these European countries set up such an organization is nothing more than to improve their domestic economic development and promote the improvement of people's living standards through this organization. The most important thing is that they want to unite through such an organization to resist the threat of other external forces.
More importantly, Europe, a country with relatively small individual strength and a very small land area, will not have a high position on the international stage threatened by a hegemonic country like the United States if it is not United, so in order to enhance its voice and influence on the international stage. They established the European Union.
However, the European Union has not played a very good role. Although many countries have joined, not all countries are willing to join, such as Norway. As an old European country, Norway has its own development model, such as animal husbandry and its manufacturing industry, and its domestic population ratio is also very small, resulting in their per capita wealth and people's happiness index is very high. So Norway did not choose to join the EU.