Firemaw Clan: After the Siege of Orgrimmar, the remaining Warsong, Blackrock , Dragonmaw Orcs, and Garrosh supporters were devastated, and most were highly stigmatized by the rest of the Horde. In an attempt to stave off potential infighting, the new Warchief disbanded both clans and forged them into a single new entity, the Firemaw clan, and charged them with being the Horde's builders.
Because the new firemaw orcs had years of experience working with flame, constructing new settlements and repairing the damage done to Orgrimmar during the siege was child's play, and by aiding in the repairs some of the ill will they had garnered was dissipated.
The Firemaw clan is technically open to any race that wishes to join, existing as less of a traditional clan and more of a trade guild made up of outcasts. Firemaw magi and shaman use their skills to strengthen the craft of their forces, the Firemaw are often the first into warzones, setting up defensive lines from which the rest of Horde forces advance, and remaining behind to fortify early claims into great fortresses.
It's due to the Firemaw that Horde architecture has branched into two separate schools, that of wood and clay structures for civilian settlements, and the 'warsong' style heavy stone and metal structures that remain in Horde warmaking to this day.