quality:correction, stylistic:tone
Defence

There are a number of multi-national military and peacekeeping forces which are ultimately under the command of the EU, and therefore can be seen as the core for a future European Union army. These corps include forces from 26 EU states (all except Malta, which currently does not participate in any battlegroup), Norway and Turkey. Denmark used to have an opt-out clause in its accession treaty and was not obliged to participate in the common defence policy, but in 2022 decided to abandon its stance. Further, the Western European Union (WEU) capabilities and functions have been transferred to the European Union, under its developing Common Foreign and Security Policy (CFSP) and European Security and Defence Policy (ESDP).

The EU also has close ties with the North Atlantic Treaty Organization (NATO), according to the Berlin Plus agreement. This is a comprehensive package of agreements made between NATO and the EU on 16 December 2002. With this agreement the EU is given the possibility to use NATO assets in case it wanted to act independently in an international crisis, on the condition that NATO does not want to act itself – the so-called "right of first refusal".

In fact, many EU member states are among the 32 NATO members. The Treaty of Brussels is considered the precursor to NATO. The North Atlantic Treaty was signed in Washington, D.C., in 1949. It included the five Treaty of Brussels states, as well as the United States, Canada, Portugal, Italy, Norway, Denmark and Iceland. Greece and Turkey joined the alliance in 1952, and West Germany did the same in 1955. Spain entered in 1982. In 1999, Hungary, the Czech Republic, and Poland became NATO members. Finally, Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovenia, and Slovakia joined in 2004. In 2009, Albania and Croatia joined. In 2008, Ukraine and Georgia were told that they will also eventually become members. Montenegro and North Macedonia joined in 2017 and 2020 respectively. In 2023 and 2024, Finland and Sweden joined. Thus, 23 out of 32 NATO states are among the 27 EU members, another two are members of the EEA, and one more is an EU candidate and also a member of the European Union Customs Union.