I logged into another nation who publicly released his pass

[Calidius]

Someone publicly released one of their nation and the password to it (t6)

https://www.nationstates.net/page=rmb/postid=20341747

I couldn't help but log in, bit then I realized I would attach my history to that nation and whoever else logged into it, but it was too late. Does this mean I'm forbidden to join the World Assembly since my nation is attached with theirs too and if I join will be guilty of multiple WA accounts?

[Reploid Productions]

The nation in question isn't currently in the WA, so logging into it shouldn't cause the WA cheatscanner to ping on you. Obviously, our default line is still going to be "share nations at your own risk," but in this case the shared nation is question isn't in the WA, so that's not a concern here.

[Calidius]

The nation in question isn't currently in the WA, so logging into it shouldn't cause the WA cheatscanner to ping on you. Obviously, our default line is still going to be "share nations at your own risk," but in this case the shared nation is question isn't in the WA, so that's not a concern here.

But my history would've been attached with theirs - including their nations (so they must have a WA account somewhere)

[Reploid Productions]

The nation in question isn't currently in the WA, so logging into it shouldn't cause the WA cheatscanner to ping on you. Obviously, our default line is still going to be "share nations at your own risk," but in this case the shared nation is question isn't in the WA, so that's not a concern here.

But my history would've been attached with theirs - including their nations (so they must have a WA account somewhere)

Bit more complicated than that, especially if they login to it again. Once again, sharing nations is risky and we don't advise doing it.