Where does “左様ならば” come from?

左様ならば (Japanese) comes from Japanese ならば, from Japanese ば, from Japanese は, from Old Japanese は.

Ancestry of “左様ならば”, step by step

左様ならば traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Japanese	ならば	if
2	Japanese	ば	In Modern Japanese, attaches to the kateikei, and...
3	Japanese	は	what about, where is; Inserted between two verbs...
4	Old Japanese	は	—

Step	Language	Word	Meaning
1	Japanese	左様	like that
2	Japanese	様	way, style, appearance; be like, look like, seem...
3	Middle Chinese	樣	—