Their politics were more like those of the present powers of Europe, where kingdoms seek rather to spread their influence than to extend their dominion, to awe and weaken rather than to destroy.
Under unactive and jealous princes the Roman legates seldom dared to push the advantages they had gained far enough to produce a dangerous reputation.[18] They wisely stopped, when they came to the verge of popularity.

And these emperors fearing as much from the generals as their generals from them, such frequent changes were made in the command that the war was never systematically carried on.

Besides, the change of emperors (and their reigns were not long) almost always brought on a change of measures; and the councils even of the same reign were continually fluctuating, as opposite court factions happened to prevail.

Add to this, that during the commotions which followed the death of Nero the contest for the purple turned the eyes of the world from every other object.

All persons of consequence interested themselves in the success of some of the contending parties; and the legates in Britain, suspended in expectation of the issue of such mighty quarrels, remained unactive till it could be determined for what master they were to conquer.
On the side of the Roman government these seem to have been some of the causes which so long protracted the fate of Britain.