Back on Halo Reach and Halo 3 there was a large and thriving clan community, then when halo 4 came out there was a giant shift in the community clans were split between starting on Reach and switching to Halo 4. Many large clans slowly drifted into a recruiting dry spell and eventually disbanded. I know there are still many clans out there but many well known clans and clan leaders dropped off of the Halo world. (I mean lore based clans, not necessarily lore strict clans) And now the clan community is mainly loose clan communities, not the strong clan brotherhoods like in the days of Reach and Halo 3.
Clans that I know/think died off during that time period being:
The United Nations (Not true to lore but military based off of UNSC lore) {They were around since halo 3 till just before Halo4}
NAVCOM (Ranks based off of UNSC) {Around durring Reach}
Sangheili Eminence/Sangheili Eminence Empire (Based off of Covenant lore) {Around since the beginning of Reach, and TMK fading after Halo 4}
Sovereign Guard (Sangheili clan) (Based off of Covenant lore) {I think they began in Halo 3 died off after the release of Halo 4}
The Imperial Transcending Empire (Based off of Covenant lore)
But with The Master Chief Collection coming soon will lore based clans make their return? Will the ability to play as Sangheili rekindle the communities willingness to create strong Sangheili clans?