To what does Brutus compare his inner turmoil?

Brutus compares his inner turmoil to being at war with himself.

Be not deceived. If I have veiled my look,
I turn the trouble of my countenance
Merely upon myself. Vexèd I am
Of late with passions of some difference,
Conceptions only proper to myself,
Which give some soil, perhaps, to my behaviors.
But let not therefore my good friends be grieved
(Among which number, Cassius, be you one)
Nor construe any further my neglect,
Than that poor Brutus, with himself at war,
Forgets the shows of love to other men.