Enlargement of NATO
As of 2018, NATO officially recognizes four aspiring members: Bosnia and Herzegovina, Georgia, Macedonia and Ukraine. The Federation of Bosnia and Herzegovina within Bosnia and Herzegovina has expressed willingness to join NATO, however, it faces consistent political pressure from Republika Srpska, the other political entity in the country, alongside its partners in Moscow. Macedonia has been prevented from joining the alliance by Greece, one effect of the Macedonian naming dispute. Future expansion is currently a topic of debate in several countries outside the alliance, and countries like Sweden, Finland, and Serbia have open political debate on the topic of membership, while in countries like Ukraine, support and opposition to membership is tied to ethnic and nationalist ideologies. The incorporation of countries formerly part of the Eastern Bloc and the Soviet Union has been a cause of increased tension between NATO countries and Russia.
European integration
In fact, many EU member states are among the 28 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, Croatia and Albania joined. In 2008, Ukraine and Georgia were told that they will also eventually become members. The Republic of Macedonia's application process is finished, but it is blocked by Greece. Thus, 22 out of 28 NATO states are among the 28 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.