The Tamar Pact was first formed by the Tamar family in 2235. A family of Pakistani-American heritage, the Tamars built a power base on their agricultural resources and a strong foundation of military training. This pact was bordered by the planets of Suk II, Fatima and Nox.  Formed primarily for defense, it was successful in helping its merchants fend off pirate attacks. In the years following the Exodus, several other planets would be added, including Tamar, named for the Pact's founding family, and Arcturus, which would eventually become the original capital for the Lyran Commonwealth.
In 2271, the first Terran Hegemony member-state was formed in the form of the Free Worlds League. The Federated Suns and Draconis Combine soon followed. There was inevitable pressure on the Tamar Pact to form such a state themselves with their neighbors, the Protectorate of Donegal and the Federation of Skye. The three had much in common, as all three pacts were built upon providing defense to maintain their extensive merchant trading. The Tamars feared that the Draconis Combine would soon look to expand its borders at the Tamar Pact's expense, so they certainly had a strong motivation to take part in such an alliance. In 2339, Kevin Tamar formally proposed unification with his counterparts from Skye and Donegal. Meeting on Arcturus in 2340, they eventually hammered out a tentative agreement based loosely on the system the Greeks used to rule their city-states. They adopted the name the "Lyran Commonwealth" for their new state, and they were recognized by the Hegemony at the start of the following year. Though the early years were difficult for the nascent Commonwealth, with a unstable economy and talk of secession, it eventually persevered. 
The Age of War and the Star League
The Age of War was not kind to the Tamar Pact, as many of its planets fell to the Draconis Combine. By 2445, a full fifth of the Pact was under Kuritan rule.  Later during the reign of Archon Margaret Olsen, the machinations of the Duke of Tamar resulted in a civil war which finally ended in battle on Tamar in 2505, when the new Archon Robert Steiner stripped the Tamar family of its titles and rank. It was here that House Kelswa came into power, and they held the Dukedom of Tamar for the next six-and-a-half centuries.  Indeed, the Kelswas had long been an important and loyal family within the Pact, with Prime Minister Davis Kelswa in power as early as 2364. 
The coming of the Star League in 2571 provided a tremendous boom to the economy of the Tamar Pact, and to the rest of the Commonwealth.  It also meant there were no further attacks on its worlds from the Draconis Combine. During the Reunification War the Duke of Tamar was briefly implicated in the abduction of Archon Viola Steiner-Dinesen's heir-designate, Kevin Steiner-Dinesen. He was ultimately cleared, however. 
As the various Great Houses became increasingly overt in their raiding during the Hidden Wars towards the end of the Star League era, the Tamar Pact found itself facing the brunt of the "pirate raids" instigated against the Commonwealth. The Duchess of Tamar during the mid twenty-eight century, Monique Kelswa, had only a rudimentary knowledge of military strategy, and instead appointed military advisors to help her prepare the Tamar Pact against acts of aggression. Among her policies applied across the Pact were tax breaks for defense industries and the implementation of state-sponsored grants for higher education on rural worlds within the Pact. These measures led to a steady drop in unemployment and a boom in university enrollments and made the Duchess a promising future leader in the minds of many despite her becoming Duchess at a very young age.
The Succession Wars
When the Star League fell and General Aleksandr Kerensky departed with the SLDF, the Inner Sphere was plunged into the First Succession War. Pirate attacks sponsored by Coordinator Minoru Kurita lured Lyran defenders from their border with the Combine, allowing House Kurita to conquer two worlds and heavily raid another. 
The Tamar Tigers were one of the most prestigious BattleMech regiments of this war, even conducting a major raid on Luthien, the capital of the Combine. They were nevertheless destroyed on Benjamin in an ambush.  Despite successes by units like the Tigers, the Commonwealth continued to lose worlds, particularly to House Kurita and mostly from the Tamar March. By the end of the war, they had lost more than 30 worlds. Tamar itself had been raided, and a large amount of administrative records were lost, severely damaging the Pact's economy for several years.
The following centuries of war were no more merciful to the Tamar Pact, which continued the lose planets to House Kurita. At the start of the Third Succession War, the Duke of Tamar formed the Stealthy Tigers, a private unit that officially claimed mercenary status. Although this new unit was a success, they could not prevent the further loss of worlds.
In 2908, House Steiner launched Operation Freedom, designed not only to recapture former worlds from the Federation of Skye from House Kurita, but also to distract the Combine from striking Tamar, that was as vulnerable as ever.  This second objective would ultimately fail, and in 2915, Tamar itself was invaded. Though the attackers were driven off, it was at heavy cost and the Pact capital was still vulnerable. Archon Tatyana Steiner and her high command came up with a plan to lure the dragon to continue attacking Tamar, and continually being forced back by reinforcements. Though logistically difficult, it successfully kept Tamar from Kuritan hands, and it also distracted the DCMS from hitting other worlds along the front. It remained an effective strategy for several decades. 
By 3025, though Tamar still stood, the Tamar Pact had been reduced to almost half its original size. It consisted of the Tamar Domains and the Trellshire region, and many of its worlds (including Tamar) had born the brunt of the Succession Wars. Militarily, the Pact included the Tamar Theater and the Trellshire theater. The disruption to the bureaucracy over the years had led to a high level of corruption, which the Lyran Commonwealth government was still attempting to clean up.  General Nondi Steiner herself, the sister to Archon Katrina Steiner, served as Margrave of the Tamar Theater. 
The Fourth Succession War
At the start of the Fourth Succession War, the Lyran Commonwealth Armed Forces launched Operation Gotterdammerung, the largest Lyran invasion of the Draconis Combine in centuries. Overall, this attack was an overwhelming success, as several dozen Combine worlds fell to House Steiner, most of them planets that had formerly been part of the Tamar Pact, decades or even centuries before. The 13th Rasalhague Regulars, however, intended to counter-attack rather than wait to be overwhelmed by the Commonwealth's war machine. They struck at Tamar, apparently without orders, knowing that a successful strike could demoralize the entire Commonwealth. They were opposed by the very capable Grave Walkers mercenary unit, with two heavy regiments. 
Unfortunately for the Grave Walkers, Duke Selvin Kelswa III insisted on commanding the defense. When the Duke ordered the Grave Walkers into a death trap, Colonel Dennis Merwin, the Walkers' commanding officer, knocked the Duke unconscious and placed Kelswa and his entourage under arrest. The Walkers proceeded to route the Regulars completely, with only a handful of the Kuritans surviving to surrender. Duke Kelswa, however, placed Colonel Merwin under arrest for treason, scheduling his execution for the following morning. The Lyran high command, however, pressed the Duke on the issue, pointing out his lack of military background and informing him he would be publicly court-martialed if he continued with his charges against Merwin. The Duke reluctantly released the Grave Walkers commander. 
The Federated Commonwealth
Duke Kelswa and many in the Pact were bitterly disappointed and even enraged when Archon Katrina Steiner decided to recognize the formation of the Free Rasalhague Republic, essentially giving back most of the worlds that had been conquered. The planets had been part of Kurita's Rasalhague Military District for so long, most had lost any serious cultural connection to the Tamar Pact or the Commonwealth, and instead looked to Rasalhague for its political and cultural cues. When Kelswa attempted to keep several of the worlds through force by deploying mercenaries during the Ronin Wars, it ended disastrously for him both militarily and politically. The Tamar Pact was effectively punished by the new Federated Commonwealth government in the aftermath of the Ronin Wars with increased taxes for several years. 
In 3041, the militaries of House Steiner and House Davion were combined into the Armed Forces of the Federated Commonwealth. As part of this reorganization, the Tamar Pact was militarily named the Tamar March, broken up into the Bone and Trellshire Theaters and the Tamar Theater, with Nondi Steiner's son, Richard Steiner, commanding the Tamar Theater. 
The Clan Invasion
The Clan Invasion was devastating to the Tamar Pact, which bore the brunt of the attacks by both Clan Jade Falcon and Clan Wolf. Tamar itself fell, with Duke Kelswa fighting to the bitter end. Selvin Kelswa's daughter, Morasha Kelswa inherited her father's now meaningless titles. 
By 3054, the Tamar March had been reduced to little more than a sliver of its former glory. Nevertheless, as it essentially included the entire Federated Commonwealth-Clan Occupation Zone border, it was the most heavily defended area of the Commonwealth. 
The legacy of the old Tamar Pact now lives with Duke Robert Kelswa-Steiner, son of Morasha Kelswa and grandson to the last Duke of Tamar.
Historical Tamar Pact Map Gallery
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 10
- House Steiner (The Lyran Commonwealth) (sourcebook) pp. 11-13
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 20
- House Steiner (The Lyran Commonwealth) (sourcebook) pp. 27-29
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 12
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 32
- House Steiner (The Lyran Commonwealth) (sourcebook) pp. 34-36
- Era Report: 2750, p. 81, "Monique Kelswa"
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 45
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 48
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 71
- House Steiner (The Lyran Commonwealth) (sourcebook) pp. 72-73
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 92
- House Steiner (The Lyran Commonwealth) (sourcebook) p. 118
- NAIS The Fourth Succession War Military Atlas Volume 2 pp. 67-68
- Historical: Brush Wars p. 90
- 20 Year Update pp. 16-17, 24-26
- Wolf Clan Sourcebook pp. 43-45, 64
- Objective Raids pp. 22-23
- Shattered Sphere pp. 47-51