The britannian paradox is a historic situation where in a Roman britannian governor uses the entire britannian Roman army to attack Rome, but while doing so leaves Britannia to rot.
When this happens he loses all his support back home and can't afford to pay his large army(which is the only thing giving him the ability to take Rome).
The britannian paradox played out often, but as Hegel said, all we learn from history is that we learn nothing from history.