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Swedish soldiers during a military exercise in February
Photo: Jonathan Nackstrand / AFP
Sweden became the 32nd country to join NATO.
The Swedish government had formally decided on the step shortly before.
The last outstanding step for official accession was the deposit of the accession certificate in the US State Department, which has now happened.
US Secretary of State Antony Blinken received Swedish Prime Minister Ulf Kristersson and his Foreign Minister Tobias Billström in Washington.
"Sweden is a strong democracy with a highly capable military that shares our values and vision for the world," said a US State Department press statement.
With Sweden as an ally, the USA and its allies are even safer.
Long-standing freedom from alliances has meant that Sweden, like its neighbor Finland, has had to rely on its own military capabilities.
At the same time, the two northerners have already taken part in exercises with the defense alliance - so they know how cooperation within the alliance works.
The Swedish military has, among other things, around 120 Leopard 2 tanks, which are called Stridsvagn 122 in the Scandinavian country.
In the air, it relies, among other things, on Swedish Jas 39 Gripen fighter jets.
According to military experts, Sweden's accession is particularly attractive for strategic reasons because it means that the entire Baltic Sea coast - with the exception of the coast of Russia and its exclave Kaliningrad - is NATO territory.
For example, the defense of the Baltics could be made easier in the event of a Russian attack because troops and equipment could be transported much more easily by ship via Sweden to Estonia, Latvia and Lithuania.
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