There are currently four countries officially being considered for membership of NATO (the North Atlantic Treaty Organization).
The latest, the Republic of North Macedonia, joins Bosnia and Herzegovina, Georgia and Ukraine.
Skopje is set to sign an "accession protocol" with NATO on Wednesday that begins the process of joining the alliance.
It comes after the country settled a decades-long name dispute with neighbour Greece, who had previously blocked attempts by Skopje to join.
But will the Republic of North Macedonia get the green light? What does a country have to do to be a member?
How do you join NATO?
Before a country can be invited to join NATO, it must satisfy three prerequisites to be eligible for membership:
- The country must be geographically within Europe. This is despite the US and Canada being two of NATO's founding members.
- The country must be a democracy.
- The country must have the capacity and willingness to contribute to the security of the Euro-Atlantic area.
If these prerequisites are met, the country is then invited to join the Membership Action Plan (MAP).
MAP provides tailored advice and support on different aspects of membership ranging from defence and military to political and legal issues.
Participation in MAP does not prejudge any decision by the alliance on future membership. NATO policy states that as no two countries are the same, each MAP process varies in progression and length.
Along with the Republic of North Macedonia, Bosnia and Herzegovina is also currently participating in MAP.
The next step requires all 29 members of the Alliance to sign and ratify the accession protocol. While this ratification process is ongoing, the invitee country will begin to be integrated into certain aspects of NATO’s work.
In the final step of the process, the invitee country must adapt and deposit its own bill of ratification to join NATO. For some countries, this procedure will include a national referendum, while other countries will decide through a parliamentary vote.
Once the bill of ratification is passed, the country has successfully become a NATO member.
With this acceptance however also comes financial commitment.
At the Wales Summit in 2014, NATO allies pledged to invest more and better in defence to move closer towards the goal of spending 2% of GDP on defence by 2024.
According to NATO, total defence spending of all members stood at about $957 billion (€839 billion) in 2017.
The United States' contributed $686 billion (€601 billion) which equals around 72% of the total bill for the Alliance.
What about Ukraine?
Due to Ukraine's proximity and long-standing ties to Russia, the possibility of joining the alliance has spurred controversy in both Brussels and Moscow.
Following the Russian annexation of Crimea, Ukraine made joining NATO a priority. In that timeframe, public support for Ukrainian membership in NATO has also risen greatly.
NATO confirmed to Euronews that the allies recognise Ukraine’s aspirations to join the alliance and that they stand firm in their support for “Ukraine’s right to decide its own future".
NATO expects Ukraine to continue to focus on domestic reform, by consolidating its democratic institutions and to strengthen the rule of law – ahead of the country’s presidential election set for 31 March 2019.
“We will continue to assess our support for other countries that wish to join the alliance. Our open door policy strengthens NATO and contributes to Euro-Atlantic security,” a NATO official said.
Where did NATO come from?
Following the devastation of World War II, NATO, which is headquartered in Brussels, was created to protect the people and territory of members in the Euro-Atlantic area.
The alliance was founded on the principle of collective defence, meaning that if one NATO country is attacked the others have to step in to help.
In 1949, the 12 original signatures included UK, USA, Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway and Portugal. It was part of ensuring no large-scale war would ever again take place in Europe.
The founding treaty also allowed for new members to be invited to join NATO under the condition of a unanimous agreement of all existing allies.
NATO’s ‘open door’ policy means that any country in Europe area is free to join NATO if it is prepared to meet the standards and obligations of membership.
Since 1949, the alliance has taken in 17 new members: Greece, Turkey, Spain, Czech Republic, Hungary, Poland, Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, Slovenia, Albania, Croatia and lastly Montenegro, who joined NATO in June 2017.