Late 23rd Century / Turn of the 24th Century:
The artistic, highly-cultured and deeply-spiritual Cardassian civilization faces a dire economic crisis, having depleted the resources of their home system.
Federation begins/expands colonization of systems near Cardassian space
~2305: Cardassian economy collapses or finishes collapsing completely. People starving in the streets. Cardassian military declares martial law and takes over all government offices in response to the crisis.
2305 - 2310: Cardassian military completely restructures Cardassian society. Precious historical and cultural artifacts are sold off en mass. Cardassian Union, under military direction, begins a campaign of aggressive expansion, desperately seeking resources to revitalize their economy. Military conquests quickly become an acceptable option.
2310 - 2319: Cardassians rapidly expand their territory through force of arms and aggressive colonization. Cardassian settlers begin colonizing worlds along the frontier bordering the Federation.
2310 - 2340s: Starfleet begins producing large numbers of Type-A Exclesior class starships and Miranda class starships. The Excelsior, formerly a Battleship, becomes the mainstay Heavy Cruiser of the fleet. Versatile Miranda class ships do the same in the Light Cruiser and Destroyer roles. Starfleet opts to build and update large numbers of these two ships instead of designing newer replacements.
2311: Tomed Incident occurs between Federation and Romulan Star Empire. Thousands of lives on both sides are lost in the resulting military actions. Treaty of Algeron signed to stave off all-out war. Federation makes several concessions to the Romulan Empire, including the banning of their use or development of cloaking devices, Romulans retreat into another period of prolonged seclusion.
2319: Cardassia stations military forces on Bajor, Occupation of Bajor begins
2323: New Ambassador class Battleship is launched, replacing the Type-B Excelsior as Starfleet's premier capital ship.
2324: Cardassia annexes Bajor, Bajoran government surrenders with little resistance
2320s - 2340s: Cardassian and Federation colonists continue to settle on neighboring worlds, tensions rise between the Federation and Cardassia over desputes about the exact location of the border, and which worlds belong to whom.
Cardassian leaders are trying to grab as much as they can through whatever tricks they can pull, and assume Federation is doing the same.
Federation does not seek conflict with the Cardassians, tries to avoid conflict as much as possible due to their delicate geo-political position (Federation is effectively surrounded by hostile and/or aggressive major and minor powers with military-oriented cultures or military dictatorships)
2344: USS Enterprise-C destroyed responding to a distress call from a Klingon outpost that had come under attack by four Romulan warbirds. The ferocity of the Enterprise-C crew in their valiant, solitary defense against hopelessly overwhelming enemies deeply moves and inspires the Klingon people, turning around the declining relationship between the Federation and the Klingon Empire virtually overnight. The rapidly-escalating threat of war with the Klingon Empire disappears.
2347: Tensions have risen to critical levels. Cardassians attack Federation colony on Setlik III, claiming a pre-emptive strike. Open war is declared.
2347 - 2355: Dealing with a war with the Tholians on a separate front, as well as increasing hostilities and eventually open war with the Tzenkethi and also the Talarians, the Federation fights largely a defensive war.
The aging Excelsior and Miranda class starships also limit the Federation's ability to respond in force. Though technologically and industrially inferior to the Federation, the Cardassians' newer and bigger Galor class Battlecruisers are able to stand toe-to-toe against the Federation's aging Excelsior class cruisers that form the cores of Federation battlegroups.
2349: Niagara class Battleship is launched. Faster and more durable than the Ambassador, only slightly more heavily armed than recently-refit Ambassadors. Niagaras bolster the Federation's mobile defensive and fast raiding raiding abilities, but does not provide anything new in the way of firepower.
2350: Federation treats the war as little more than a border conflict, Federation citizens still colonizing worlds in the disputed territory such as Doran V.
Cardassians begin mining the disputed Boreti Sector with gravitic mines.
2354: USS Stargazer carries truce offer to Cardassians. Cardassians attack and cripple the Stargazer after Captain Jean-Luc Picard had lowered shields as a gesture of good will, though the Stargazer manages to escape.
2355: Springfield and Cheyenne class Light Cruisers are launched. Comparable in size to an Excelsior, they sport the new massive phaser arrays allowed by recent developments in phaser technology, and bring tremendous firepower for their size onto the field.
2357: New Orleans and Challenger class Heavy Cruisers are launched, bringing even more firepower into the Federation's arsenal on much more resilient platforms. Construction of the newer cruisers ramps up and they begin replacing Excelsiors on the front line, vastly bolstering Federation military strength.
2355 - 2360: Having diverted much of their expansion efforts into the war with the Federation, and suffering major setbacks with the deployment of newer Federation cruisers and other advanced military equipment, the war begins to take a major toll on the Cardassian economy, which was already brittle to begin with.
Federation war with the Tholians comes to an end, though hostilities and tensions remain high.
2360: Responding to the deficiencies of the aging Ambassador and the already-outdated designs of the Niagara, Starfleet begins a two-ship design program and rapidly develops and launches the Nebula class, an absolutely massive Battleship featuring much of the technology and advancements developed shortly after the launch of the Niagara, which are now off-the-shelf tech.
Already weakened by the great success of Starfleet's new cruisers and their faltering economy, Cardassian military is quickly out-matched by the new Nebula class Battleships, even with the limited number that could be deployed initially.
Cardassian economy goes into crisis again. Cardassian military operations against the Federation drop to little more than skirmishes and the occasional raid.
Despite their new advantage, Federation does not press the attack against the Cardassians, who interpret this to mean that the Federation is actually weaker than they appear.
2363: The Galaxy class Battleship, sister to the Nebula in Starfleet's two-ship capital ship design program, is launched. Featuring state-of-the-art, bleeding-edge technology, the Galaxy surpasses the Nebula in performance in all areas despite being the same size.
Federation still does not advance into Cardassian territory. Though wars with the Tholians, Tzenkethi and Talarians are over, and the new alliance with the Klingon Empire is going strong, the Federation's geo-political situation is still strenuous, and a military offensive into Cardassian is very unpopular.
2367: An armistice is signed between the Federation and Cardassians, bringing the already-dwindling war to a halt. Though not technically a formal end to the war, both sides view the war as being over.
2367 - 2370: Despite their technological and military superiority, the weakened state of the Cardassian military, and the dire state of crisis of the Cardassian economy, the Federation does not press the Cardassian Union in the peace talks, and makes several concessions to the Cardassians even though the Cardassians initiated the hostilities, and repeatedly violated the terms of the armistice on several occasions, including an attempt to take Minos Korva in 2369. Federation diplomats are painfully aware of their geo-political situation, and how distasteful renewed conflict with the Cardassians, let alone the prospect of an offensive war against Cardassia, is to the Federation Council.
The Federation does win some concessions from the Cardassians, however, such as the Cardassian withdrawal from Bajor in 2369, after 50 years of occupation.
2370: Formal peace treaty is signed, De-Militarized Zone is established over the disputed area, forbidding weapons and significant starships from either side to enter. Several Federation colony worlds are ceded to the Cardassians.
Cardassians begin arming their colonists in the DMZ almost immediately after the treaty is signed.
Federation citizens in the DMZ, outraged by what they feel is inadequate defense by the Federation during the war, and inadequate Federation responses in the face of Cardassian attrocities and violations of the armistice and peace treaty, take up arms in response to being forced from homes they built with their own sweat and blood, and then defended for 20+ years, at the end of a war they effectively won. Supported by Bajoran resistance fighters and sympathetic members of Starfleet on all levels, they brand themselves the Maquis and begin active armed resistance operations against the Cardassians.
2370 - 2373: Tensions between the Federation and Cardassia fluctuate, and cooperative attempts are made, but conflicts with the Maquis resistance in the DMZ as well as continued Cardassian violations of the peace treaty keep tensions and resentment high on both sides. The discovery of the Bajoran Wormhole and access to the Gamma Quadrant spark new tensions, as do events surrounding the arrival of the Dominion.
2373: Hostilities renewed as the Cardassian Union throws in with the Dominion and war breaks out once again.