urbe, i.e. the capital.
eget ille is opposed to nos suppeditamur, the contrast being emphasized by the omission of the connecting particle and the arrangement of the words (Chiasmus).
causas ipsas quae, etc., 'simply the causes which are arrayed against one another.'
velimus, subj. because in the apodosis 'intelligere possumus' is equivalent to the potential subjunctive 'intelligamus.' Cf. [1. 2] 'satisfacere videmur, si vitemus,' and [note].
iaceant. See [on 2. 2].
denique aequitas, etc., sums up the preceding; the four cardinal virtues (justice, temperance, bravery, wisdom) are set against the corresponding vices. The antithesis must be carefully kept in translation.
bona ratio cum perdita, 'upright against corrupt principles.'
mihi, dative of agent. See on [1. 16].