The Mark of the Sentinel was the first dragonmark to appear, and was used by the noble family on who they manifested to compliment their natural fighting prowess. The Deneith clan was able to conquer most of the region in and around what would become Karrnath. If it weren’t for a famine that struck the area, there is a good chance that they would have been able to establish a kingdom of their very own. Who knows, the House Deneith could have been known as the kingdom of Deneith if it wasn’t for them not being to feed their troops.
Though not a member of the house, Karrn the Conqueror was born in clan Deneith's homeland. He created the nation of Karrnath, which was one of the first human established nations on the soil of Khorvaire. It was then that House Deneith pledged their fealty of Karrn, and helped him wage war in an unsuccessful attempted to unite all of the five settlements of Khorvaire beneath him. Even with Hosue Deneith’s assistance, he was unable to achieve this goal, but it solidified Hosue Deneith as a military force to be reckoned with. Years later Galifar rose to power and became ruler of Karrnath. Galifar was able to succeed where Karrn could not, unifying the Five Nations of Khorvaire. It was after the unification that he charged House Deneith to be the protectorate of the Five Nations.
The Last War was the next rung on the climb to greatness for House Deneith. Having pledged to serve the entire kingdom that Galifar I had created, they would do so even without a king or queen to rule it. This allowed them to be completely neutral during the conflict, but it did not stop them from supplying mercenaries to each of the five nations when such a request was made. It’s interesting because this in stride by the warring nations, knowing that while they may have the forces of House Deneith fighting for them, their enemies were doing the same thing. House Deneith went to great lengths to make sure that the mercenaries from their house did not come into direct conflict with each other, but war is a rapidly enveloping situation and there is one recorded instance of this happening. A Cyran general ordered a group of mercenaries from the blademarks guild to attack a Deneith guarded garrison. When they refused, the general order his Cyran troops to attack the blademarks who refused to fight, which was a very bad idea indeed. These blademarks joined forces with the forces from within the garrison and routed the Cyran troops.
When the war finally came to an end with the signing of the Treaty of Thronehold, House Deneith was granted several concessions not available to the other houses. They were granted an exemption from the Korth Edicts and were only the house among the Twelve allowed to maintain a standing army. Furthermore, members of House Deneith and their forces could travel freely amongst the Five Nations. While nations may have fiercely guarded there borders from their neighbors, House Deneith members were granted free passage in the name of defending the Five Nations from external (and sometimes internal) threats.
Within the House, there have always been two guilds and three primary services that they provide. The House Deneith mercenaries hail from the Blademarks Guild and their reputation as an elite fighting force was cemented during the Last War. Since the rule of Galifar I, the Defenders Guild has protected the wealthy and powerful, which included nobles and kings. Finally, there are the Sentinel Marshals, who uphold the law of the land throughout Khorvaire, are have a storied history.
Sentinel Marshals have been the elite in law enforcement in Khorvaire for centuries. Marshals uphold the code of justice no matter where it may take them, pursuing criminals across national borders and beyond. Centuries prior, King Galifar III commanded the patriarch of House Deneith to form an elite order of officers who would augment the royal guard in maintaining the peace, upholding the law, and bringing those who broke the law to justice. Taking heirs of the house that had proven themselves through years of service within the house, the Sentinel Marshals were assembled and their name invoked respect amongst the people, and fear for those that broke the law. In the years before the Last War, the Sentinel Marshals became the police force to be reckoned with, working to bring those within the kingdom of Galifar that worked outside the law to justice, and eliminating the enemies of the crown outside of its borders.
During the Last War, the Marshal’s focus was less on bringing criminals to justice and instead on maintaining the rules and conduct of war. The Marshals also took it upon themselves to enforce the Galifar code of justice, insisting that each of the warring armies observe these universal rules of conduct even during the war. At the end of the Last War, the Sentinel Marshals remained as the enforcer of the code per the Treaty of Thronehold. The right of free passage for House Deneith allowed the Marshals to hunt down criminals throughout the five nations without interference.