Though the deal has effectively been done for weeks, the tiny Balkan nation of Montenegro formally joined NATO today, becoming the alliance’s 29th member, and its first new member in nearly a decade. Croatia and Albania were the last NATO members to join, on April 1 of 2009.

Montenegro’s accession was a controversial one, as the nation is domestically split heavily over the issue, with the nation’s historic ties and heavy financial ties to Russia making many fear that they risk losing much by joining NATO. NATO’s attack on them during the Kosovo War is also still a sore spot for many.

Montenegro’s Prime Minister made his first appearance at a NATO event last month, and was immediately involved in a highly publicized incident, in which President Trump shoved him out of the way during his own arrival at the meeting.

The US was the last of the NATO nations to grant Montenegro’s accession, doing so earlier this year. the State Department praised the move today, insisting that the US remains committed to the NATO alliance, as well as the principle of collective defense among alliance members.