(Not sure if this is the right place for this, so please move if not so.)
Specifically, Fascist states for now, although I'll consider including others for another list, perhaps with authoritarian leftist states, like with Stalinism or Maoism, for another list.
1. US: While unlikely, it's still possible, especially if FDR died. A US Fascism, based on the KKK, would've been incredibly hard to dislodge, and the world would probably have to wait until it burns out before it's ever defeated.
Weaknesses: Perhaps in tactics and internal dissent from relatively large size of abused groups.
Advantages: Include resource self sufficiency, plenty of manpower to draw from, a massive industrial base, and incredibly hard to invade with two oceans separating it from any power that could hope to oppose it.
Targets would probably include,
a. Anything in the Western Hemisphere(easy targets, along with racism against Hispanics.)
b. UK, along with rest of Commonwealth with it perhaps.
c. Any Communist country.
2. Russia: What's terrifying about this one is how it would've only required the Whites won. Then, a combination of slavic nationalism with religious extremism, and a need for elites to get a new ideology would result in a Fascist state with many expansionist aims.
Advantages: General Winter, along with a harsh climate in general will make it a pain to invade. Massive manpower base means it can't be bled dry like Germany or Japan was in OTL. Resource self sufficiency means it can't be starved like Germany or Japan was in OTL.
Disadvantages: Lack of industrialization perhaps, along with problems of modernization. Massive resources to control territory already conquered.
Targets:
a. Balkans, and similar places with Slavs, with theme of Slavic nationalism.
b. Japan for the loss in the Russo-Japan war, and by extension, territories like Manchuria.
c. Germany for issues it caused in during WW1, including sending the Communists like Lenin.
d. Any Communist country.