Difference between Yakuza 0 and Yakuza 6

Sometimes I see Asian lives of Ryu ga gotoku 6 (an opus of yakuza). Interested by the game I decided to see if I could order it, but the only one available is Yakuza 0. I quite don't understand what's the link between those two games. Is Yakuza 0 an American edition of Ryu ga gotoku 6 or another game?

Yakuza 0 and Yakuza 6 are two separate games simply put the major difference between the two is that Yakuza 0 is a prequel to the entire series which takes place before Yakuza 1. Yakuza 6 will be the most current game in the Yakuza series taking place after Yakuza 5. So yes both games are completely separate games.