Denmark learned the hard Way, after centuries of neutrality politics, unless they had any interest in a conflict, that neutrality is not Well respected. They declared neutrality prior to World War 2, but less than a year after the invasion of Poland, it was Denmark that became occupied.

Thanks to the Danish Ambassador in Washington during the war, who decided to defy the Nazi friendly politics of the Danish Government, the Foundation for a close alliance between Denmark and the US was established and the US helped Denmark rebuild their military. As Well as help create the Royal Danish Airforce, which has been a huge asset to NATO. Denmark was therefore convinced it was the right thing to do, to join NATO when it was founded in 1949 and they are therefore considered a founding member. So the query about
Is Denmark part of NATO is now may be cleared.