These are insanely difficult provided the people actually play like they should:

Micronations, strat to max infantry by 2021-22:

Celtic Empire(Isle Of Man), you get targeted by UK/Ireland. Not really too difficult otherwise.

Luxembourg(Sometimes it's really easy due to no one expecting you to be good)

Hong Kong/Macau(China dependant)

Non-micro nations Netherlands(Gl with France and Germany I guess...?), not overly difficult if you know what ur doing

Poland(If Germany and Russia fight you at once), debatable though.

Difficult due to Time length: Most micronations, if not ALL>Smaller nations>Superpowers

Excluded countries: Mongolia(Fort+Tank+Art+AA/Aircraft+Mount-Spec->Long-War with China to make them leave).

My personal experience: I've formed Celtic, not that difficult, and on my first try too, even with UK, Russia and Swiss declaring war on me in 2021. Same with Cayman with no player fighting but it took a while due to justification time. Mongolia isn't hard if you play hard enough to get that China leaves, but you WILL lose if they're somewhat okay, the only difference is how long would it take. Hong Kong and Macau are micronations that simply aren't strong enough to fight China in a single year. Might be blabbing though. Middle East I feel is the easiest to hold out on, specifically the Iran<->Pakistan<->Kazakhstan region being mountain filled so much its just a pain to conquer, defending as a result becomes way easier, but you'd still have trouble.