Genshin Impact World & Story Primer: the 7 Nations, the Seven, and the Khaenri'ah Cataclysm

The game currently has 6 of the 7 element-linked nations open, plus an 8th region (Nod-Krai) not tied to one fixed element; the 7th nation (Snezhnaya, Cryo) is not open yet:

See every character grouped by nation (team role, rarity, element) on the full character list.

The Archon War — the war for the divine thrones — ended roughly 2,000 years ago; the winner in each nation became its Archon and received a Gnosis, a chess-piece-shaped item confirming divine status and allowing direct resonance with Celestia, the highest heaven where the gods live. It was later revealed the Gnoses were made from the remains of the "Third Descender." A Vision is something else entirely: bestowed by Celestia and the Seven upon a small minority of ordinary people with sufficiently strong desires, letting them channel an elemental skill matching that Vision's element — this is exactly the kind of Vision the Traveler and most party members carry in-game.

Khaenri'ah is the only one of the 8 nations with no Archon. Roughly 500 years ago it was destroyed in a single cataclysm when the Abyss broke into Teyvat — the event known as the Khaenri'ahn Cataclysm. Because it had no Archon, almost no official record of the nation survives in Teyvat's present-day history; most of what players learn comes out gradually through story quests. Separately, Irminsul — a giant tree woven into the foundations of the earth, enduring since the dawn of the world — is said to hold the totality of Teyvat's knowledge and memory across the ages, including what was erased from Khaenri'ah's official record.