Sweden has officially become the 32nd member of Nato, Prime Minister Ulf Kristersson has confirmed.
Kristersson handed over the final documentation to the US government, the last step in the process to secure the backing of all members to join the military alliance.
US Secretary of State Antony Blinken said: "Good things come to those who wait...This is a historic moment for Sweden, for our alliance and for the transatlantic relationship."
For Nato, the accessions of Sweden and Finland, which shares a 1,340 km border with Russia, are the most significant additions in decades. It is also a blow for Russian President Vladimir Putin who has sought prevent any further strengthening of the alliance.
Sweden has become the 32nd member of the alliance
Reuters
Sweden will benefit from the alliance's common defence guarantee under which an attack on one member is regarded as an attack on all.
Blinken added: "The reason this is such a strong, powerful fit, is because Sweden embodies and promotes the core values that are at the core of Nato- democracy, liberty, the rule of law."
PM Kristersson said: "Unity and solidarity will be Sweden's guiding lights as a Nato member. We will share burdens, responsibilities and risks with our allies."
"We will defend freedom together with the countries closest to us – both in terms of geography, culture and values."
US Secretary of State Antony Blinken welcomed Sweden's ascension to Nato
Reuters
While Stockholm has been drawing ever closer to NATO over the last two decades, membership marks a clear break with the past, when for more than 200 years, Sweden avoided military alliances and adopted a neutral stance in times of war.
After World War Two, it built an international reputation as a champion of human rights, and since the Soviet Union collapsed in 1991, successive governments have pared back military spending.
Researcher at defence think tank SIPRI Barbara Kunz said: "Joining NATO is really like buying insurance, at least as long as the United States is actually willing to be the insurance provider."