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.
1997 Madrid summit
The topic of enlargement was the main focus of the summit. The result of the summit was that Hungary, Poland, and the Czech Republic were invited to join NATO. Fellow Visegrád Group member Slovakia was excluded from this invitation. Slovakia had held a referendum on NATO membership in May 1997, but turnout in the referendum failed to achieve the required 50% of eligible voters and government sabotage was blamed, which in turn was viewed as one of a string of undemocratic measures taken by Prime Minister Vladimír Mečiar. A majority of NATO members reportedly supported France's proposal to also immediately invite Romania and Slovenia as members, but this was strongly opposed by U.S. President Bill Clinton, and even a "iron-clad guarantee" that they could be invited in two years time was watered-down in favor of an "open door" policy for new potential members. A main concern for the United States was the cost of potentially raising the military standards of the new Eastern European members. Estimates put this cost at as much as $10 billion USD, which participants worried could lead to the treaty recognizing the new members being rejected by the Republican-held U.S. Senate. Additionally, a "Charter on a Distinctive Partnership" was signed between NATO and Ukraine, creating the NATO-Ukraine Commission and establishing relations between the two, and a declaration supporting peace efforts in Bosnia-Herzegovina was read and signed by participants.