NATO has today cleared Sweden and Finland to join the military alliance after the countries applied following Russia's invasion of Ukraine.
This becomes one of the biggest shifts in European security in decades, after Vladimir Putin's invasion of Ukraine pushed Helsinki and Stockholm to drop their tradition of neutrality.
According to a summit statement, NATO's 30 allies took the decision at their summit in Madrid.
There, they also agreed to formally treat Russia as the "most significant and direct threat to the allies' security".
"Today, we have decided to invite Finland and Sweden to become members of NATO," NATO leaders said in their declaration, after Turkey lifted a veto on Finland and Sweden joining.
After hours of talks between the leaders in Madrid on Tuesday, Turkish President Tayyip Erdogan agreed with his Finnish and Swedish counterparts a series of security measures to allow the two Nordic countries to overcome the Turkish veto.
These were imposed by the Turkish capital of Ankara in May due to concerns about terrorism.
Despite the swift decision to invite the countries, ratification in allied parliaments is likely to take up to a year.
However, once it has been done, the neighbouring countries will be covered by the NATO's Article 5 collective defence clause - putting them under the United States' protective nuclear umbrella.
Speaking about the decision, Secretary General of NATO, Jens Stoltenberg, said: "We will make sure we are able to protect all allies, including Finland and Sweden".
The NATO secretary-general also added that Russian tyrant Vladimir Putin is now "getting more NATO on his borders".
In the meantime, the allies are set to increase their troop presence in the Nordic region. There will be an increase in "high readiness" troops, Stoltenberg says.
"Together, this constitutes the biggest overhaul of our collective deterrence and defence since the Cold War," continued Stoltenberg.
"We will transform the NATO Response Force and increase the number of our high readiness forces to well over 300,000."
The general also added that the 30-member alliance is expected to consider Russia to be "the most significant and direct threat to our security".
Echoing his words, Belgian Prime Minister Alexander de Croo said that Russia's invasion of Ukraine is "a direct threat to our Western way of life," as he cited the wider impact of the war, such as rising energy and food prices.
At today's NATO summit, the alliance agreed a longer-term support package for Ukraine - in addition to the billions of dollars already pledged in weapons and financial support.
German Chancellor Olaf Scholz said that arms would continue to be supplied to Kyiv, adding: "The message is: We will continue to do so - and to do this intensively - for as long as it is necessary to enable Ukraine to defend itself."
The Western alliance also put forward an agreement that big allies such as the United States, Germany, Britain and Canada will pre-assign troops, weapons and equipment to the Baltics and intensify training exercises.
Following today's decision, it is feared that Putin could lash out at NATO - particularly at Latvia, Lithuania and Estonia - which were once ruled from Moscow.
The NATO Response Force is currently around 40,000 soldiers, sailors and air personnel.
