Denmark is treated as a hesitant member in the EU because it chooses four opt-outs in the Maastricht Treaty. Specifically to the field of Defense, it is the only country that opts out of EU defence policy. However, as a relatively small country that depends on the western alliance’s support in the defence, it seems unreasonable to Denmark to choose opt-out in the defence policy. Current literature put much effort into explaining Danish opt-out in the field of EMU and JHA, lack the focus to the defence policy. More importantly, when negotiating the draft of the Maastricht Treaty, the Danish government already accepted the discourse about the CFSP and CSDP and agreed to postpone the final decision to defence cooperation at the end of the 1990s. But, getting through the first failure of the referendum, the defence was listed on the issue that asking for the opt-out to the EU. It leads to the question: why Denmark choose opt-out from EU defence policy? This paper would like to use the process tracing to trace back the Danish involvement in the EC and EU, especially during the negotiation of the Maastricht Treaty, to finds out the cause of Danish opt-out in the defence. It argues that the Danish opt-out in CSDP is a result of adapting to the identity dispute. There are two major disputes during the negotiation periods, one among the political elites, one between the elites and the public. The dispute among the political elites was eased by the external change, but the public cannot change its mind so quickly as the elites which lead to reverse to government’s attitude towards the defence cooperation.
