Where does “なのだ” come from?

なのだ (Japanese) comes from Japanese だ, from Japanese である, from Japanese で, from Japanese ぜ, from Japanese ぞえ, from Japanese え, from Middle Chinese 衣.

なのだ (Japanese): used to indicate a strong assertion

Definitions

なのだ traces back through 3 separate lines of ancestry.

Step	Language	Word	Meaning
1	Japanese	だ	Following parts of speech that do not inflect by...
2	Japanese	である	To be: the copula, with the same function as だ and its polite form です
3	Japanese	で	at; with, by, using; indicating the following...
4	Japanese	ぜ	sentence-ending particle signifying emphasis,...
5	Japanese	ぞえ	sentence-ending particle signifying emphasis, used to lightly press one's point, with affectionate overtones
6	Japanese	え	Alternative form of い
7	Middle Chinese	衣	—

Step	Language	Word	Meaning
1	Japanese	の	genitive case marker; nominative case marker in a...
2	Old Japanese	の	plain, field
3	Middle Chinese	能	talent, ability

Step	Language	Word	Meaning
1	Japanese	な	used to get someone's attention, generally...
2	Japanese	ね	emphasis and question marker particle; asks for...