I’m a dual citizen (Canada & USA, born Canadian). Part of naturalization in the US is the oath where you renounce citizenship from everywhere else. Thing is, most countries don’t care about that oath–Canada requires filing a special form and appearing before an official (IIRC) to renounce citizenship. I asked about the discrepancy–it turns out the US doesn’t actually care whether I’m a citizen elsewhere, largely because it’s difficult to figure it out and enforce it (this might have been the opinion of the immigration officer, not sure).