They destroy Vulcan because the Romulans desire to destroy all Federation Planets for vengeance. More? AnswerParty!!
United Federation of Planets
Star Trek is an American science fiction entertainment franchise created by Gene Roddenberry and currently under the ownership of CBS and Paramount. Star Trek: The Original Series and its live action TV spin-off shows, Star Trek: The Next Generation, Star Trek: Deep Space Nine, Star Trek: Voyager and Star Trek: Enterprise as well as the film seriesStar Trek make up the main canon. There has also been Star Trek: The Animated Series.
Westerns such as Wagon Train, along with the Horatio Hornblower novels and Gulliver's Travels, inspired Roddenberry when he created the first Star Trek. It followed the interstellar adventures of James T. Kirk and the crew of an exploration vessel of a 23rd-century galactic "United Federation of Planets" — the EnterpriseStarship . This first series, now referred to as "The Original Series", debuted in 1966 and ran for three seasons on NBC. These adventures continued in the short-lived Star Trek: The Animated Series and six feature films. Four spin-off television series were eventually produced: Star Trek: The Next Generation, followed the crew of a new Starship Enterprise set a century after the original series; Star Trek: Deep Space Nine and Star Trek: Voyager, set contemporaneously with The Next Generation; and Star Trek: Enterprise, set before the original series, in the early days of human interstellar travel. Four additional The Next Generation feature films were produced. In 2009, the film franchise underwent a relaunch with a prequel to the original series set in an alternate timeline titled simply Star Trek. This film featured a new cast portraying younger versions of the crew from the original Enterprise. A sequel to this film, Star Trek Into Darkness, premiered on May 16, 2013.
The United Federation of Planets, usually referred to as "the Federation", is a fictional interplanetary federal republic composed of planetary governments depicted in the Star Trek television series and motion pictures. The planetary governments agree to exist semi-autonomously under a single central government based on the principles of universal liberty, rights, and equality, and to share their knowledge and resources in peaceful cooperation and space exploration.
In those episodes and films, the Federation is described as an interstellar federal polity with, as of the year 2373, more than 150 member planets and thousands of colonies spread across 8,000 light years of the Milky Way Galaxy and taking the form of a post-capitalist liberal democracy and constitutional republic. It has also been described as a utopian socialist society.]according to whom?[ The Federation is described as stressing, at least nominally, the values of universal liberty, equality, justice, peace and cooperation. The Federation also maintains its own quasi-militaristic and scientific exploratory agency, known as Starfleet (also written as "Star Fleet" in some texts). Starfleet is seen handling many other governmental processes, sometimes with no other agency's influence, such as border defense, diplomatic envoy and has seen extensive use as an offensive military force.]citation needed[
Yesterday's Son is a novel by A. C. Crispin set in the fictional Star Trek Universe. It describes the events surrounding Spock's discovery that he has a son. Yesterday's Son and its sequel, Time for Yesterday, make up A. C. Crispin's Yesterday Saga.
The book was the first Star Trek novel other than the movie novelizations to make the New York Times Bestseller List.