After being demilitarized in 2005, Sweden re-introduced permanent troops to Gotland in 2016, following Russia’s annexation of Ukraine’s Crimean Peninsula in 2014. Sweden also became NATO’s newest member in March — meaning it is covered by the alliance’s Article 5 guarantee that all other members come to each other’s defense if they are attacked.
By some accounts, Russia would need to take Gotland before they could besiege the Baltic States. Though that doesn’t mean they’d have a good chance of succeeding.