Guild Tiers are divided into Bronze, Silver, Gold, and Master. They are:
 
Bronze III -  Bronze II - Bronze I
Silver III -  Silver II - Silver I
Gold III -  Gold II - Gold I
Master
 
Tap on the Guild Wars button on the Guild Screen or  tap the Guild Wars button on the Mission Hub to find more information about the current tier of your guild.
 
Tier reset
 
At the start of each season, the Victory Points and Reward Points are reset.

Your Guild Rank will be brought down to a lower one, based on your guild's ranking in the previous season. This helps increase the competitiveness of the initial wars and allows guilds to achieve their true rank more quickly.

Your Guild’s all-time Victory Point totals can be seen on the Leaderboards, which can be seen by tapping the “Leaderboards” button on the Guild Wars section of the Guild Screen.