Storyline
According to the fictional storyline of the Star Trek universe, the Bajorans are an ancient species who developed advanced technology prior to the evolution of humanity on Earth. They eventually developed space-faring ships, which took them as far away as the planet of Cardassia. In 2328 the Cardassian Union, which had been taken over by a military dictatorship, invaded Bajor, occupying it for forty years, during which time they forced many Bajorans into slave labor, using them in their various mining operations. This forced many Bajorans to flee and live in refugee camps away from Cardassian domination, while other Bajorans got involved in the resistance movement, organising terrorist attacks against Cardassian targets.
The Federation could not intervene in the situation, due to Prime Directive considerations; since Bajor had formally aligned itself with the Cardassians some time before, it was considered an internal matter between the Cardassian Union and a member/subject planet. This caused some resentment towards the Federation by the Bajoran people, especially when the Federation was initially invited to administer Deep Space Nine.
In 2369, the Cardassian civilian authorities ordered the military to withdraw from Bajor, after which the Bajoran provisional government invited the United Federation of Planets to set up base on the former Cardassian mining station of Terok Nor, renaming it Deep Space Nine, and requesting membership into the Federation.
In 2369, when Commander (later Captain) Benjamin Sisko was assigned command of DS9, one of his instructions was to prepare Bajor for full membership into the Federation (pilot episode: "Emissary"). This was a long-running theme during the rest of the series. In 2373, with the Dominion War on the horizon, Bajor asks to be admitted to the Federation under special circumstances. Sisko, acting as Emissary of the Prophets, warned that if Bajor were to join the Federation at that time, it would mean the destruction of that world. With this warning, Bajor decided not to accept membership at that time. At the start of the Dominion War, Bajor officially declared their neutrality ("Call to Arms"), although many Bajorans joined Starfleet and, as well, a new resistance to the occupation of Deep Space Nine is formed. According to the novel series Star Trek: Titan, Bajor finally formally joined the Federation in 2376, the year after the Dominion War ended.
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