Read Card. Manning's excellent Christ and Antichrist : a sermon at the mass of Requiem for those who fell in defence of Rome [against the Freemasons] (1867):

…it is well for them to know that the Catholic world, neither now nor hereafter neither at the decease of Pius IX., nor yet at any time—will yield one shadow of the inalienable right of the Sovereign Pontiffs to the capital of Christendom; nor will it for a moment suffer the denial of its own supreme right and duty to intervene for the protection of the Holy See. The moral cordon of justice and order will be always drawn around it; and the right of execution will never depart from the Catholic world.

If only the Masonic occupation of Rome forced the 2nd Vatican Council to end, rather than the 1st Vatican Council! (I suppose it was so occupied by Freemasons that it ended before it even started, since it's hardly a Catholic council.)

Another good one is his The temporal power of the pope in its political aspect (1866):

All I can do is to touch the mere outline of what would follow upon the dissolution, if that could be, of the Temporal Power of the Pontiffs. But first let me once for all, or rather once more for the thousandth time, sweep away the absurdity imputed to us, day by day, that we make the Temporal Power a part of Christianity, and that if it were overthrown, Christianity would fall with it. This surpasses even the extravagance of controversy. We do believe, indeed, that the dissolution of the twofold authority of the Pontiff would strike out the key stone of Christendom; that is, of the twofold order of Christianity and civilization which for a thousand years has sustained the commonwealth of Europe. We believe that then Christianity would stand alone, on its own divine and imperishable basis; and that civilization without Christianity would return to the natural order, and to the spiritual death out of which Christianity raised it to life.

[…] We affirm also that this retrogression and divorce of the spiritual and civil societies of the world would desecrate the civil powers of the world. They would cease to recognise, as they have already to a great extent, the Christian law, the unity of faith, worship, communion, or authority, as principles of their public order. […]

[…] The two powers, spiritual and temporal, are providentially united in Rome that they may be separated everywhere else in the kingdoms of the world. […]

Temporal power of the vicar of Christ (1862) — Card. Manning, free on Archive.org is also entitled The Temporal Sovereignty of the Popes, The present crisis of the Holy See, The last Glories of the Holy See.

Also, The present crisis of the Holy See tested by prophecy — Card. Manning—entitled by TradiBooks, The Pope and The Antichrist—has been mentioned a few times on the fora as a "must read" (cf. this and this thread).

Another good Card. Manning book is The temporal mission of the Holy Ghost : or, Reason and revelation (1865).  For the modern-day relevance of this book, read this or this.