NATO foreign ministers welcomed tiny Montenegro into their fold on Wednesday in the alliance’s first expansion since 2009, Reuters reports.

Jens Stoltenberg, the head of Nato, said it was a “historic decision,” according to BBC.

While Montenegro has now been invited to join NATO, it can take up to 18 months for a country to formally join. NATO diplomats say membership is likely to be cemented at the summit of alliance leaders next July in Warsaw.