Albania had a good try, but lacked the industrial base to do much harm beyond laying mines in the Adriatic.
Tito's Yugoslavia could have gone 'To The Dark Side' as he struggled to elude the USSR's grasp. Instead, all the bottled-up grudges 'blew off' later...
Had the Manhattan Project been restricted to a few, semi-tactical, Uranium 'gun-type' bombs, and the Japanese not, um, 'Seen The Light' per OTL, perhaps. If the US took a really bloody nose(*) on first phase of invasion, they might decide the main islands would be far, far too costly, decide to 'attrite' them instead. By the time US fire-bombers have razed everything above 'large village', the islands are semi-Medieval on the surface, with craft work-shops & small factories underground, total dispersal, total paranoia...
(*) Murphy's Law rampant, aka ' Gallipoli#2': Anzio break-out failure, Normandy beach mistakes, the weather turning nasty, a tsunami (!!), 'Human Wave' attacks by civilians shielding kamikase troops etc etc etc...
Several South American countries swung unto 'crazy'. Argentina's Junta made a good try, were very nearly at war with Chile before invading the Falklands. Chile's Pinochet' death-squads killed a LOT of by-standers while fighting the rabid Marxists and, um, vice-versa. If Ernesto "Che" Guevara had not died in Bolivia, he might just have carved a paranoid Marxist enclave out of the border zones...
Cuba was in the running, but the Castro brothers seem to have kept the place 'borderline sane' by force of personality. Sending Che off to make mischief else-where surely helped...
Could Venezuela yet 'lose the plot' ?? IMHO, NO, the borders are too open...