The simple reason is that the Concordant has always had a uneasy relationship with the Federated Suns going back six centuries. This means that it varies from wariness to out and out paranoid.
When Sharplin took the leadership role, he saw Davion spies hiding behind every tree. His sate of mind wasn't help by the Word of Blake, who were running the Concordant's HPG stations. The Concordant had always considered the Pleiades Cluster theirs, even though they hadn't controlled them for centuries.
So, Duke Hasek decides to invades the Confederation. Sharplin decides that raids against Davion would be a good idea (Whether or not the Word influenced this mindset is open to discussion). The raids happen, the Concordant troops find the Davion garrisons are gone, so they turn the raids into occupations. One of those worlds was Bromhead, where they massacred two thousand dependents of Hansen's Roughriders.
To make it short, the Roughriders stamped a few Concordant formations into paste, and the Concordant backed off. Then the Concordant capital was obliterated by asteroids, and the evidence pointed to the Davions. The Concordant launch a full-scale invasion, throwing nukes around at the slightest hint of resistance. The Davions managed to get enough forces together to halt the Concordant and face them back. A few years after the Jihad, the Davion grabbed most of the Concordant border worlds (Though the Concordant hung onto the Pleiades) and forced the Concordant to sue for peace. Now in the Dark Age, the Concordant is a military dictatorship with a weak military and paranoid in the extreme
Craig
