The details of the Occupation and the Federation/Cardassian border wars has never been pinned down exactly, but it goes something like this:
Bajor was an artistic and very spiritual culture before the Cardassians developed warp drive and the Bajorans were originally the ones to make contact with the Cardassians using solar-sail style ships (season 3, Explorers). The Cardassians were also a very artistic culture with a strong focus on family values, but they were impoverished by a lack of resources and their society began to fall into a shambles. In response there was some sort of coup and the military took control of the government, they expanded the Cardassian Union in order to attain the resources they needed to feed the people. One of the worlds they conquered was Bajor some time in the 2310s because it was rich in mineral deposits. They put in place an occupational government of Bajoran collaborators, but the Cardassian military held nearly all the power.
In 2346 the Cardassians used Bajoran slave labour to build Terok Nor (later renamed Deep Space Nine by Starfleet) and this was used as an orbital ore refinery and the seat of Cardassian military power. The occupation began to get out of control due to Bajoran resistance fighters using guerilla tactics, so around 2360 Gul Dukat was put in charge of the occupation with the task of getting the planet under control. He wanted the Bajorans to love him and supposedly tried to end the resistance through peaceful means, but under his rule the resistance and occupation got worse (season 6, Waltz).
Odo was found in the Denorious belt (near the wormhole which had not been discovered yet) in 2337 and was trained by a Bajoran scientist called Mora Pol into mimicking the humanoid form (season 2, The Alternate). He did some investigative work on Bajor and developed a reputation as an impartial figure who had no loyalty to the Cardassians or Bajorans, so Gul Dukat recruited him to investigate a murder on the station (season 2, Necessary Evil). This led to him meeting Kira for the first time and Dukat decided to keep him as the full-time police chief on the station.
The Federation/Cardassian border wars ran between the 2340s to the 2360s and seem to be based on Cardassian attempts to annex worlds with Federation colonies, probably in an attempt to acquire resources. O'Brien was involved in a particularly nasty incident when the Cardassians attacked Setlik III and this experience haunts him for the rest of his life (TNG season 4, The Wounded). The border wars never seemed to erupt into a full-scale conflict, it was mainly contained to skirmishes along the border. A ceasefire was eventually reached, but in 2369 the Cardassians decide to make a another attempt at annexing some border worlds in the Minos Korva incident. Starfleet managed to prevent the invasion before it began (TNG season 6, Chain of Command Parts 1 & 2).
The Minos Korva incident seems to have been a huge blow to the Cardassians, and mixed with the increased pressure from the UFP government for the Cardassians to end the occupation of Bajor, and the failure of Dukat to crush the resistance, Bajor proved too costly to maintain as part of their Union so the Cardassians withdrew. They damaged a lot of the infrastructure during the withdrawal, including Terok Nor, so the Bajoran provisional government contacted the Federation and asked for assistance. Starfleet decided to send a team headed by Sisko to Bajor in order to administer the space station and act as a liaison to their government. And that's where Emissary kicks off...
Bajor was an artistic and very spiritual culture before the Cardassians developed warp drive and the Bajorans were originally the ones to make contact with the Cardassians using solar-sail style ships (season 3, Explorers). The Cardassians were also a very artistic culture with a strong focus on family values, but they were impoverished by a lack of resources and their society began to fall into a shambles. In response there was some sort of coup and the military took control of the government, they expanded the Cardassian Union in order to attain the resources they needed to feed the people. One of the worlds they conquered was Bajor some time in the 2310s because it was rich in mineral deposits. They put in place an occupational government of Bajoran collaborators, but the Cardassian military held nearly all the power.
In 2346 the Cardassians used Bajoran slave labour to build Terok Nor (later renamed Deep Space Nine by Starfleet) and this was used as an orbital ore refinery and the seat of Cardassian military power. The occupation began to get out of control due to Bajoran resistance fighters using guerilla tactics, so around 2360 Gul Dukat was put in charge of the occupation with the task of getting the planet under control. He wanted the Bajorans to love him and supposedly tried to end the resistance through peaceful means, but under his rule the resistance and occupation got worse (season 6, Waltz).
Odo was found in the Denorious belt (near the wormhole which had not been discovered yet) in 2337 and was trained by a Bajoran scientist called Mora Pol into mimicking the humanoid form (season 2, The Alternate). He did some investigative work on Bajor and developed a reputation as an impartial figure who had no loyalty to the Cardassians or Bajorans, so Gul Dukat recruited him to investigate a murder on the station (season 2, Necessary Evil). This led to him meeting Kira for the first time and Dukat decided to keep him as the full-time police chief on the station.
The Federation/Cardassian border wars ran between the 2340s to the 2360s and seem to be based on Cardassian attempts to annex worlds with Federation colonies, probably in an attempt to acquire resources. O'Brien was involved in a particularly nasty incident when the Cardassians attacked Setlik III and this experience haunts him for the rest of his life (TNG season 4, The Wounded). The border wars never seemed to erupt into a full-scale conflict, it was mainly contained to skirmishes along the border. A ceasefire was eventually reached, but in 2369 the Cardassians decide to make a another attempt at annexing some border worlds in the Minos Korva incident. Starfleet managed to prevent the invasion before it began (TNG season 6, Chain of Command Parts 1 & 2).
The Minos Korva incident seems to have been a huge blow to the Cardassians, and mixed with the increased pressure from the UFP government for the Cardassians to end the occupation of Bajor, and the failure of Dukat to crush the resistance, Bajor proved too costly to maintain as part of their Union so the Cardassians withdrew. They damaged a lot of the infrastructure during the withdrawal, including Terok Nor, so the Bajoran provisional government contacted the Federation and asked for assistance. Starfleet decided to send a team headed by Sisko to Bajor in order to administer the space station and act as a liaison to their government. And that's where Emissary kicks off...