Before we begin the fifth book of our history, we must beg those who may peruse this treatise, not to censure us too hastily because having set out to write a church history we still intermingle with ecclesiastical matters, such an account of the wars which took place during the period under consideration, as could be duly authenticated. For this we have done for several reasons: first, in order to lay before our readers an exact statement of facts; but secondly, in order that the minds of the readers might not become satiated with the repetition of the contentious disputes of bishops, and their insidious designs against one another; but more especially that it might be made apparent, that whenever the affairs of the state were disturbed, those of the Church, as if by some vital sympathy, became disordered also. Indeed whoever shall attentively examine the subject will find, that the mischiefs of the state, and the troubles of the church have been inseparably connected; for he will perceive that they have either arisen together, or immediately succeeded one another.
Sometimes the affairs of the Church come first in order; then commotions in the state follow, and sometimes the reverse, so that I cannot believe this invariable interchange is merely fortuitous, but am persuaded that it proceeds from our iniquities; and that these evils are inflicted upon us as merited chastisements, if indeed as the apostle truly says, 'Some men's sins are open beforehand, going before to judgment; and some men they follow after.' For this reason we have interwoven many affairs of the state with our ecclesiastical history.
Of the wars carried on during the reign of Constantine we have made no mention, having found no account of them that could be depended upon because of their iniquity: but of subsequent events, as much information as we could gather from those still living in the order of their occurrence, we have passed in rapid review. We have continually included the emperors in these historical details; because from the time they began to profess the Christian religion, the affairs of the Church have depended on them, so that even the greatest Synods have been, and still are convened by their appointment.
Finally, we have particularly noticed the Arian heresy, because it has so greatly disquieted the churches. Let these remarks be considered sufficient in the way of preface: we shall now proceed with our history.
Source: Ecclesiastical History (New Advent)