The Tholians are highly xenophobic and generally limit contact with other races. Humans had never heard of the Tholian homeworld, Tholia, until 2151, when a reference to Tholia was made in the record of a Klingon courier named Klaang, who was carrying information regarding the Suliban Cabal. (ENT episode & novelization: Broken Bow)
The Assembly did have some limited interaction with Vulcans before the 2150s and made first contact with a Human vessel, Enterprise, in 2152. This early Human interaction with the Tholians led to conflict as the Tholians gained knowledge that Enterprise was in possession of future technology, which they tried to steal. The Tholian Assembly's interest in time travel was indicative of their suspected involvement in a larger conflict, the Temporal Cold War. Though they were a party in the attempted stealing of the futuristic shuttle, they did not actually harm or try to harm the Vulcans or the Enterprise crew. (ENT episode: "Future Tense")
First contact between the Assembly and the Federation was made by the USS Intrepid, which was performing a deep space charting mission near the disputed Tholian border. The commanding officer of the Federation starship was warned by the Tholians to leave the area immediately, after which Captain Spiak of the Intrepid complied, whereupon he informed Starfleet Command of the encounter. Several weeks later, a transmission from the Tholians demanded an audience with Captain Spiak at the border line as the Assembly thought it was prudent to learn more about the nature of a possible enemy. (TOS reference: The Worlds of the Federation)
Relations between the Assembly and Humanity did not improve after this first hostile encounter. By the 23rd century, the Tholians were involved in frequent conflicts with the United Federation of Planets in their expansionist programs. The Tholians, who have a non-humanoid makeup incompatible with environments humanoids occupy, were known during this era to employ shock troops of cultures they had conquered or conscripted into their service. One of the most feared of the Tholians' enforcers were the Chakuun species. (EV comic: "Flesh of My Flesh")
Ongoing conflict with the Federation was finally brought to an end in 2254 when there was a revelation regarding the differences in the way the two powers measured borders and territory. (EV comic: "The Fallen")
Tholians expanded into the Taurus Reach (which they referred to as the Shedai sector) in response to the return of the Shedai. This expansion led them into a conflict which resulted in the vicious destruction of the USS Bombay. Through the efforts of station crew at Starbase 47, war was prevented. (Star Trek: Vanguard novels)
In 2268, the Tholian Assembly ordered the destruction of a Klingon colony on Taelus II. The USS Defiant was carrying proof of this back to the Federation, when it received a distress call from an interphasic rift. The rift had been created in 2155 by the Tholians in the mirror universe in an attempt to lure in a ship from their future. The Defiant disappeared into the rift, but not before the USS Enterprise arrived to assist. Tholian vessels were dispatched to drive the Enterprise from Assembly space. (TOS episode: "The Tholian Web"; ENT episode: "In a Mirror, Darkly"; SCE eBook: Interphase)
- It is unclear what, if any, relationship existed between the 23rd century Tholians and their 22nd century mirror universe counterparts. The temporal nature of such a relationship might imply this is yet another tangle in the web of the Temporal Cold War.
Ongoing contact with the Federation was minimal. The Assembly rarely contacted the Federation, but they did slow their expansion and ceased encroaching on Federation territory. Better relations between the Assembly and the Federation opened in 2298, after the Federation intervened in a conflict between the Tholians and the Neyel Hegemony being conducted over extradimensional tunnels between the Milky Way Galaxy and the Small Magellanic Cloud created by the interphasic rift. (TLE novel: The Sundered)
In 2262 of the Kelvin timeline, the Tholians' armada, under Commander Loskene, then captured the USS Enterprise when it experienced effects from Interphase. Loskene claimed that the Enterprise had violated their borders and attempted to take them to Tholia to answer for their crime. The Enterprise then escaped, but Loskene stated that a state of war now existed between the Federation and the Assembly.(TOS - The Tholian Webs comics: "Part 1", "Part 2")
Relations between the Tholians and the Federation remained tense throughout the 24th century. In 2353, the Tholians destroyed a Federation starbase and the Tholians were often factored into Starfleet simulations and tactical analysis of potential Tholian involvement in other conflicts. (TNG episodes: "The Icarus Factor", "Peak Performance", "Reunion")
Tholian space was violated in 2367 when a doomsday machine under the command of a woman known as Delcara entered their territory in order to "devour" worlds within their space to power the weapon. Attempts were made to stop her, but even the infamous Tholian web weapon was incapable of halting the behemoth. Fortunately it was stopped thanks to the assistance of the crew of the USS Enterprise-D. (TNG novel: Vendetta)
In 2371, Tholian colonies were attacked by a splinter group of Hugh's independent Borg, using the Taj, a stolen Klingon bird-of-prey. This triggered Tholian reprisals against the Klingon Empire and the Federation, nearly plunging the three powers into war. Commander William Riker and First Officer Nethrax joined forces to find the Taj and the rogue Borg were turned over to the Tholians for judgment. (TNG comic: "War and Madness")
The Tholians were interested in controlling the Bajoran wormhole and Captain Benjamin Sisko considered them to be one of several possible factions involved in the conflict between Bajor and the Ferengi Alliance in 2372. (DS9 novel: The 34th Rule) They also often pursued Razka Karn for unspecified reasons. (DS9 episode: "Indiscretion")
In 2373, the Tholian Assembly signed a non-aggression pact with the Dominion, and stayed uninvolved through the entirety of the Dominion War. (DS9 episode: "Call to Arms") This combined with the tenuous peace they had with the Federation meant that the Assembly were content with observing the war. However, whilst an unpopular opinion publicly, some believed that the Tholians would have fallen before the superior might of the Dominion had the Founders not been defeated. (SCE eBook: Interphase, Part One)
In 2376, the Defiant reappeared. The USS da Vinci was sent to retrieve it, and several Tholian starships oversaw it. However, when proof that they had performed the massacre at Taelus was discovered, the Tholian Assembly ordered the destruction of the da Vinci. They were fought off and forced to retreat however, by the joint powers of the da Vinci and the Defiant. SCE eBook: Interphase)
- This appears, at first glance, to contradict ENT episode: "In a Mirror, Darkly", in which the Defiant is transported to the mirror universe and captured by the Terran Empire. However, the authors of the Interphase SCE stories are currently collaborating with "In a Mirror, Darkly" writer Mike Sussman to create an ENT-era mirror universe story that will be a sequel to "Darkly," suggesting a possibility that this story arc will be closed, reconciling the two stories' endings.
The USS Trident, USS Excalibur and the USS Enterprise were key to the revelation of Selelvian telepathic manipulation on the Federation Council. This revelation led to the Federation revoking Selelvia's membership. In retaliation, the Selelvians allied themselves with the Tholian Assembly and a short war between the Federation and the Selelvians was the result. (NF novels: Stone and Anvil, After the Fall; NF short story: "Pain Management")
In 2381, the Tholians were the senior partners in an alliance with the Gorn, Breen, Tzenkethi, Kinshaya, and the Romulan Star Empire. This alliance, known as the Typhon Pact, was formed with the intent to exploit the weakening of the Klingon Empire and United Federation of Planets by the Borg in their final invasion and just before their dissolution and absorption into the Caeliar Gestalt. The forming of the Typhon Pact was the catalyst for a meeting between the Federation, Talarians, Klingons, Cardassians, Ferengi, and the Imperial Romulan State (an offshoot of the RSE) to discuss the widening of the Khitomer Accords into a general alliance to protect against the Typhon Pact. (see Star Trek: Destiny trilogy and the follow-up novel A Singular Destiny).