Oda tells the readers which nationality the Strawhats might have in the real world and a fan asked this question and Oda replied Japanese for Zoro!
As we all are the same opinion, that Wano are based on ancient Japan, the possibility for Zoro having his roots there getting a bit higher,We know Ryuma from Wano is the same Ryuma from Oda’s previous one-shot manga, Monsters. And when we look at his appearance :
He looks almost like Zoro, only the black hair and his Samurai hairstyle are different,he even eats one of Zoro’s favorite attacks “Onigiri”.Ryuma is also left handed just like Zoro, because Samurai have their swords on the right hip when they are left handed!
Zoros behavior is just like that of an Samurai, even Vivi gave him the nickname Mr. Bushido. Bushido is the codex/credo of Samurais, a guide of how they live etc.
People might say, a lot of Swordsman are like that, but that’s false, he really acts like a Samurai and that’s not a coincidence, because I believe Oda plans big things with him in Wano!