Bötticher's "Historiae Antiquae Epitome" (p. 127/128)

[Carolus Raeticus]

Salvete!
I'm currently reading Bötticher's "Historiae Antiquae Epitome", a 300-page (Latin only) history book "in usum scholarum". Most of it is fairly easy to read, but there a few passages which give me a bit of trouble. The following (about the fall of the last Roman king L. Tarquinius Superbus) is one of them:

Sed exhausto magnificentia publicorum operum aerario quum [sc. L. Tarquinius Superbus] Ardeam Rutulorum caput obsideret, urbem divitiis praepollentem, ut praeda deliniret plebem, praeter aliam superbiam ideo etiam infestam regno, quod se tamdiu servili exercitam opere a rege indignabatur, Sexti Tarquinii pessimum facinus paratos iam omnium ad seditionem animos ad evertendam regiam dominationem impulit.

Most of this passage is fairly straightforward. The bit printed in bold, however, gives me considerable difficulty, though. A (deliberately) quite literal translation might be like this:

But when the treasury had been emptied by the greatness of the public works and he [L. Tarquinius Superbus] was besieging Ardea, capital of the Rutuli and very powerful due to its wealth, so that with the booty [gained in the conquest of Ardea] he might mollify the common people, which was dangerous to his royal power for the reason (besides his haughtiness) that it [sc. the people] resented having been employed in a slavish work for such a long time by the king, the extremely foul crime of Sextus Tarquinius drove the minds, already ready for a rebellion, to overturn the royal power.

Why "praeter aliam superbiam" and not simply "praeter superbiam"?
What about the rest of the bold passage? Am I getting it right? Somehow it doesn't feel quite right (mostly I do not translate in my head).

Can anyone help me?

Valete,

Carolus Raeticus

[adrianus]

[alius -a -um] B. In comparisons, with atque, ac, or et, more rarely with nisi and quam; with the latter, in good class. authors, only when preceded by a neg. clause, or by an interrog. implying a neg.; cf. Ruhnk. ad Ter. And. 3, 3, 13; instead of quam, the comp. abl. or praeter, and similar words, sometimes appear, other than, different from, etc.

verbatim (ut puto) // literally (I think) "due [not just] to [yet] a further [/another] arrogance [by Tarquin the Proud/Arrogant], [but] on account of one also threatening the kingdom, since it [the populous/mob] was resenting itself [being] subjected for so long to slave labour by the king"

[thesaurus]

Do you have a copy of the book, or are you reading it online? I'd like to have a look at it myself.

[Carolus Raeticus]

Salve Thesaure!

Sorry, that I'm only replying now. If you haven't yet found it, you can download it from this Google-books page

I like this book as its difficulty level is consistent, beyond the mere entry level stuff but still accessible.

Vale,

Carolus Raeticus