Cataclysm

Comparable to the Permian-Triassic Extinction on Earth, the Cataclysm of Cardassia Prime is a climate shift and mass extinction event believed by Cardassian scientists to have begun as the result of global warming triggered, at its beginning, by a sharp increase in volcanic activity, which led to a serious increase in greenhouse gases in the atmosphere of Cardassia Prime. Increased temperature, extinctions, and desertification in some areas have been observed effects of the Cataclysm. Severe loss of farmland, especially on the continent of Hăzăk, triggered mass starvation among the Cardassian people. (--"Point of Divergence," "Cardassian Sunrise")

The Cataclysm had severe social ramifications to the Cardassian (then "Hebitian") people. A poorly-organized governmental response to the people's mass suffering exacerbated the long-simmering discontent of individuals who disagreed with the religious-based government. A revolution led by Tret Akleen eventually toppled the Hebitian government and led to the establishment of the dictatorial Cardassian Union.

In an alternate universe, Guide Yavenn Pretam helped to settle the unrest among the people, to reform the government, and influence the Castellan to find a way to move Cardassia forward. By necessity, Cardassia explained its situation and opened trade relations with its neighbors that helped sustain it as colonization efforts expanded and also helped to sustain the Cardassian homeworld that--at least, on its own--could not support its population while still in the throes of the Cataclysm.

Earth comparison
Extinction events of this sort can take millions of years to play out, with devastating effects on the affected planet. The Permian-Triassic extinction on Earth was responsible for killing almost all of Earth's therapsids, the ancestors of Earth's mammals, and the creatures most similar to the Cardassians themselves (who, while not completely identical to Earth's pre-mammalians, are referred to by xenobiologists as "therapsids").