Unification
Unification or union (as in, a political union) was the joining of two or more entities (i.e. species or governments) into a single entity for the first time. Union, though, may also be taken to mean an altogether separate term, most notably during a time of war, alliance. () 

Following the elimination of the Ekosian's Nazi regime on Ekos in 2267, followed by their predicted cooperation with the neighboring Zeons, Spock recommended that "With the union of two cultures, this system would make a fine addition to the Federation." () In fact, the Federation itself was a union of planets, and as according to Admiral Charlie Whatley, "it's much more than that", so stated at the ceremony marking the first attempt to admit Bajor into the Federation in 2373. () Retired Vice Admiral Norah Satie also shared those sentiments, having once described the United Federation of Planets as "extraordinary union" that she so wished to see preserved. () Hologram Janeway also described the Federation as "an interstellar union of different worlds and species, with shared principles of universal liberty." ()

After decades of civil war, Mordan IV finally became unified in 2319, in fact, according to Captain Jean-Luc Picard, Governor "Karnas was largely responsible for the planet's unification and peace." ()

Examples of political unions 
 Cardassian Union
 Confederate States of America
 Eminian Union
 Union of Soviet Socialist Republics
 United Federation of Planets
 United States of America

Reunification 
Reunification was the re-joining of two or more entities into a single entity that were previously unified, such cases included the Irish Unification of 2024 (); in other cases these events were simply described as a unification. ()

Vulcan-Romulan reunification 

The reunification of the Vulcans and Romulans was primarily driven by or supported by the government and citizens of the Romulan Star Empire, both officially and unofficially. From as early as the late 21st or 22nd century, the Romulans, in part through their agent Talok, attempted to manipulate the Vulcan High Command through Administrator V'Las. Although their initial plan failed in 2154, Salok promised that "The reunification of our people is only a matter of time." ()

Almost 150 years later, the future-Ambassador Spock forged a friendship with the Romulan Senator Pardek at the Khitomer Conference. Decades later, Spock revealed to Captain Picard that for some time a Romulan underground movement was growing, by Romulans who wished to embrace "the ideals of the Vulcan philosophy." Although the Romulan government was subversive to the idea, Pardek, one of the underground movement's few sympathizers therein, invited Spock to Romulus, believing that "it may be time to take the first step toward reunification." Thought Spock thought it unlikely to succeed, he could not "ignore the potential rewards that a union between our two worlds would bring." ()

During what was to be the first step, a face-to-face meeting with Proconsul Neral, Spock found the Romulan leader highly supportive of the cause, stating that he believe that "it must eventually come", because "Our two worlds need each other." After Neral assured Spock that he could convince the Romulan Senate to support the initiative, thus leading to a public endorsement of the cause, Spock, who was on Romulus on his own accord, stated that the Vulcan people "will be cautious" as "There are generations of distrust [for them] to overcome." Indeed, Spock later stated that Sarek, his father, "would have seen this mission of reunification as a fool's errand", while Spock felt that it was not. ()

When it was eventually revealed that the entire plot was a scheme to reveal the underground, lead in part by Romulan military Commander Sela, she explained that things had changed, and that "Your dream of reunification is not dead. It will simply take a different form. The Romulan conquest of Vulcan." This was to be carried out by an invasion force sent to  on board stolen Vulcan ships, in the guise of a peace envoy. Sela believed that once the troops reached Vulcan, the Federation would have a hard time reacting because "we will be there, entrenched, and it will be very difficult to get us out once we are. Reunification will become a fact of life." Though the Romulan invasion force was ultimately subverted, Spock, nonetheless felt that, "The union of Vulcan and the Romulan people will not be achieved by politics or by diplomacy, but it will be achieved." ()

Centuries after Spock's death in the 24th century, the Vulcans and Romulans were reunified. In the early days, the Qowat Milat, an ancient Romulan sect who lived and died by the Way of Absolute Candor, were essential in building trust between the two tribes. As they learned to share the planet Vulcan, the first Romulo-Vulcans were born from the union of Vulcans and Romulans. The name of the planet was changed to Ni'Var.  

In the late 31st century, Ni'Var became independent from the Federation in the wake of The Burn. The Romulans, wanting to remain in the Federation, opposed secession. Over the next century, tensions increased among the factions, with unrest in provinces with Romulans and insurgencies in Romulo-Vulcan regions. ()

Xindi reunification 

The Xindi Council was formed following the destruction of Xindus. Their goal was to reunify the Xindi by, first, locating and agreeing upon new homeworld before their plans were put on hold when they learned of the threat from Earth, cause the prelude of events which lead to the Xindi incident. () Near the climax of these events, Dolim became suspiciously agreeable with Degra, as both were often conflicted members of the Xindi Council, regarding the interference caused by the Earth ship . Dolim assured Degra that rest of the Council will fall into line, while claiming that "I have always believed that all Xindi long for unification. It's in our blood." ()

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