Cardassian War
The Cardassian War was a conflict in the mid 24th century between the United Federation of Planets and the Cardassian Union.
The details of this war are sketchy at best. What we do know is the war must have only been fought on a limited basis and it ended with a negotiated settlement with the Cardassians. This settlement was not very logical with the Federation seceding colonies to the Cardassians and the Cardassians seceding ones to the Federation.
As part of this settlement the Cardassians demanded that Federation citizens inside the new territory be evacuated leaving the planets to be populated entirely by Cardassians. The Cardassians did move their citizens but Federation colonists were very reluctant to leave their homes. Those that remained formed the core of what would become the Maquis.