The official entry of Croatia was marked on 1 April 2009 by the deposition of Croatia's ratification instrument of accession to the North Atlantic Treaty to the U.S. State Department since the USA is depository for the North Atlantic Treaty. The ratification instruments were officially handed by the then Croatian Ambassador to the USA, Kolinda Grabar-Kitarović.
Croatia and Albania were jointly admitted to the alliance as the 28th and 29th member states.
After the ratification of the accession protocol in the parliaments of member states and in Croatia's parliament on 25 March 2009, then NATO secretary-general Jaap de Hoop Scheffer sent Croatia an official invitation to join the alliance on 30 March that year.
Institutional relations between Croatia and NATO were established in 2000 through the Partnership for Peace (PfP) programme and preparations for membership were launched in 2002 with the Membership Action Plan (MAP).
The political decision to invite Croatia and Albania was adopted in April 2008 at the summit in Bucharest and the decision was brought to Zagreb from Romania's capital by the then president of America, George Bush.
Speaking in Zagreb’s St. Mark’s square on 5 April 2008, President Bush promised that no one would be able to deprive Croatia of its freedom any more.
2008 Initiative for launching referendum on NATO membership fails
In 2008, an initiative was launched for calling a referendum on Croatia's entry into the alliance. Referendum Initiative Committee spokesman Aleksandar Hatzivelkos said at the time that they planned to collect 10% of the signatures of all eligible voters to force Parliament to call a referendum under the Constitution.
Members of the NATO Referendum Committee said that they were neither for nor against Croatia's entry, but stressed that they believed citizens had the right to express their opinion on the matter in a referendum.
The referendum petition was signed on 2 April 2008 by the then Opposition leader, Social Democratic Party (SDP) president, Zoran Milanović, who said at the time that his party advocated Croatia's NATO entry, but that it also believed that politicians and citizens together had to make this important and far-reaching decision.
However, the petition was not supported by the required number of signatures and the initiative failed.
Croatians support membership, 7 in 10 are in favour of being part of NATO
According to the latest opinion poll conducted by NATO in its member-states in the last two month of 2023, as many as 72% of Croatian would vote for the continuation of the country' membership of NATO, if a referendum were to be conducted on the matter.
Croatia's inclusion in NATO missions
Before its official entry into the alliance, Croatia started participating in NATO-led operations and missions. For instance, Croatian troops were engaged in the ISAF operation in Afghanistan from 2003 to 2015 and also from 2015 to 2020 in the NATO-led mission Resolute Support Mission (RSM).
Croatia's contingents are participating in NATO-led missions in Kosovo (KFOR) and in NATO Enhanced Forward Presence (eFP) in Poland and Lithuania and in NATO enhanced Vigilance Activity in Hungary. Furthermore, two Croatian officers are being engaged in Iraq.
Until May 2023, Croatia's Navy was included in the NATO-led Sea Guardian operation in the Mediterranean.
Croatia spent 1.75% of its GDP on defence in 2023
Croatia is among the NATO member states that have still not reached the set defence spending target of 2% of GDP, and according to an estimate for 2023, it spent 1.75% of its GDP on defence in that year.
Croatia was closest to the 2% allocation in 2021, when it paid the highest installment for the purchase of the Rafale fighter jets, amounting to 1.97% of its GDP. In 2022 the allocation dropped to 1.79%.
The NATO Secretary-General has recently published the 2023 report on military spending with details on defence allocations by the member states.
The year 2023 was the ninth consecutive year in which the member countries, on the whole, increased defence budgets, by a record 11%.
In the period between 2014 and 2023, according to prices from 2015, Croatia increased its defence budget from US $892 to US $1.136 billion, an increase of 27.5%.
In 2014, Croatia's defence spending per capita was USD 210, and in 2023 this is set to have reached USD 291.
As for the structure of defence spending, Croatia meets the target of a minimum 20% of defence budget being spent on equipment. According to the estimate for 2023, Croatia spent 23.9% of its defence budget to procure equipment. Poland spent the most for that purpose, 53.9%, followed by Finland, with 50.8%.
Alliance marking its 75th anniversary
The 15th anniversary of Croatia's admission coincides with the 75th anniversary of the establishment of NATO. On 4 April 1949 state secretaries for foreign affairs of the USA and Canada plus foreign ministers of 10 European countries -- Belgium, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal and the United Kingdom -- signed the North Atlantic Treaty in Washington, and thus became the founding members of NATO.
The first round of enlargement happened in 1952 with the admission of Greece and Turkey. In 1955 the West German followed their suit. In 1982, Spain joined the alliance.
After the Cold War, Czechia, Hungary and Poland joined the alliance in 1999, as the first ones from the former Warsaw Pact.
In 2004, the alliance admitted seven new members: Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia.
After the alliance welcomed Croatia and Albania in 2009, the next round of enlargement ensued in 2017, with Montenegro joining the alliance, and in 2020 North Macedonia.
The newest members are Finland (2023) and Sweden (2024), which applied for the membership when Russia led by President Vladimir Putin launched a war of aggression against Ukraine.
Article 5
The key section of the treaty is Article 5 with its commitment clause defining the casus foederis.
Article 5 commits each member state to consider an armed attack against one member state, in the areas defined by Article 6, to be an armed attack against them all. Upon such attack, each member state is to assist by taking "such action as [the member state] deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."