When Russia invaded Ukraine on February 24, the security policy situation in Europe changed radically.

Ten days later, the news came that the Danish people will have a referendum on participating in the EU's full defense cooperation.

"There was a time before Russia's attack on Ukraine and there is a time after," said Prime Minister Mette Frederiksen (S) on the evening of March 6, when she and several opposition parties held a press conference on holding a referendum.

Today, around 4.2 million Danes can vote on the defense reservation - one of four exceptions to EU co-operation that Denmark has had since 1993. Of the parliamentary parties, only the red-green Unity List and the immigration-critical Danish People's Party and Nye Borgerlige say no to taking removed the exception.

- For the Danish People's Party and Nye Borgerlige, it is about Denmark's sovereignty in relation to the EU.

For the Unity List about a militarization, says Rasmus Brun Pedersen, senior lecturer in political science at Aarhus University.

Enough with NATO - the parties believe

However, the right to rule over Danish soldiers will not be handed over to the EU if the reservation is lifted.

It is the Danish parliament that decides whether soldiers should be included in future EU operations. 

However, both the Danish People's Party and Nye Borgerlige believe that it is enough for Denmark to join the NATO defense alliance. 

- When we talk about security, it is NATO that guarantees our security, independence and freedom, said recently Pernille Vermund, party leader for Nye Borgerlige, according to the news agency Ritzau.

For a long time, it has not been a major problem for Denmark to stand outside the EU's defense cooperation, but after Russia's annexation of Crimea in Ukraine in 2014, the Union has taken small steps towards deeper cooperation in this area.

- It has become more and more times where our reservation has been noticed.

Several times where we have not been able to attend, for example, various meetings.

It did not mean much until 2014, because the EU did not have much activity in the area before that, says Brun Pedersen.

Did not matter

Although the Danish exception has become more noticeable in recent years, it has in practice not had any significance, says Peter Viggo Jakobsen, senior lecturer at the Danish Defense College. 

- The EU is a small military player, so for that reason it does not matter whether we are involved or not.

The reservation means that we can not take part in operations led by the EU, but there we have instead compensated by contributing to other operations in NATO and the UN, he says.