Scarlet Crusade

The Scarlet Crusade (also known as the Scarlet Brotherhood (or simply the Crusade) is a fanatical religious sect that evolved from the Knights of the Silver Hand, dedicated to the eradication of the undead from Lordaeron. A major adversary of the Forsaken and Scourge, their name has become synonymous with corruption and extremism, and several quests in Tirisfal Glades involve attacks on Scarlet Crusade troops, leaders, and strongholds. The Scarlet Crusade maintains several bastions throughout the former lands of Lordaeron, namely the Scarlet Monastery, and up until the Cataclysm - Hearthglen, Tyr's Hand, the fortified Scarlet Bastion of Stratholme, and several smaller camps and scout towers spread throughout the whole area of northern Lordaeron.

It is one of the hierarchies left over from the kingdom of Lordaeron after its destruction by the Scourge. After the attack on the Scarlet Enclave, the Scarlet Crusade renamed itself to the Scarlet Onslaught and operated in Northrend, though some members of the original Scarlet Crusade did not transfer to the Scarlet Onslaught.

Since the fall of the Lich King, the Scarlet Crusade has experienced a downfall, losing many of its holdings in the now-recovering Plaguelands to the Argent Crusade, and many of its surviving members, ironically, to undeath as the Risen.

During the third invasion of the Burning Legion, the remnants of the Scarlet Crusade in Lordaeron regrouped at the Monastery under the command of High Commander Goodchilde, they were soon assaulted by the Knights of the Ebon Blade who totally wiped them out, in order to resurrect Sally Whitemane as a member of their new Four Horsemen. In Northrend, while the Scarlet Onslaught was largely dismantled and originally stated to be the replacement for the Crusade, New Hearthglen continues to operate, even though it has lost the majority of its leadership and its goals have been dashed away, and was interchangeably referred as the Crusade and as the Onslaught.

As of the end of the Fourth War, the "Scarlet Brotherhood" was formed, marking a resurgence of the Scarlet ideology in Lordaeron, they declared themselves to be House Menethil loyalists and were politically opposed to the Alliance, which they saw as being led by a traitor.

See https://wowpedia.fandom.com/wiki/Scarlet_Crusade for now.