From Dom Guéranger's The Liturgical Year.
God promised Noah that He would never more punish the earth with a deluge. But, in His justice, He has many times visited the sins of men with a scourge which, in more senses than one, bears a resemblance to a deluge: the invasion of enemies. We meet with these invasions in every age; and each time we see the hand of God. We can trace the crimes that each of them was sent to punish, and in each we find a manifest proof of the infinite justice wherewith God governs the world.
It is not requisite that we should here mention the long list of these revolutions, which we might almost say make up the history of mankind, for in its every page we read of conquests, extinction of races, destruction of nations, and violent amalgamations, which effaced the traditions and character of the several peoples that were thus forced into union. We will confine our considerations to the two great invasions, which the just anger of God has permitted to come upon the world since the commencement of the Christian era.
The Roman Empire had made itself as preeminent in crime as it was in power. It conquered the world, and then corrupted it. Idolatry and immorality were the civilization it gave to the nations which had come under its sway. Christianity could save individuals in the great empire, but the empire itself could not be made Christian. God let loose upon it the deluge of barbarians. The stream of the wild invasion rose to the very dome of the Capitol; the empire was engulfed. The ruthless ministers of divine justice were conscious of their being chosen for this mission of vengeance, and they gave themselves the name of ‘God's scourge.’
When, later on, the Christian nations of the east had lost the faith which they themselves had transmitted to the western world; when they had disfigured the sacred symbol of faith by their blasphemous heresies; the anger of God sent upon them, from Arabia, the deluge of Mahometanism. It swept away the Christian Churches, that had existed from the very times of the apostles. Jerusalem, the favoured Jerusalem, on which Jesus had lavished His tenderest love, even she became a victim to the infidel hordes. Antioch and Alexandria, with their patriarchates, were plunged into the vilest slavery; and at length Constantinople, that had so obstinately provoked the divine indignation, was made the very capital of the Turkish empire.
And we, the western nations, if we return not to the Lord our God, shall we be spared? Shall the flood-gates of heaven's vengeance, the torrent of fresh Vandals, ever be menacing to burst upon us, yet never come? Where is the country of our own Europe, that has not corrupted its way, as in the days of Noah? that has not made conventions against the Lord and against His Christ? that has not clamoured out that old cry of revolt: Let us break their bonds asunder, let us cast away their yoke from us? Well may we fear lest the time is at hand, when, despite our haughty confidence in our means of defence, Christ our Lord, to whom all nations have been given by the Father, shall rule us with a rod of iron, and break us in pieces like a potter’s vessel. Let us propitiate the anger of our offended God, and follow the inspired counsel of the royal prophets Serve ye the Lord with fear; embrace the discipline of His Law; lest, at any time, the Lord be angry, and ye perish from the just way.
We find the following beautiful words in the Ambrosian liturgy for Septuagesima. They occur in the missal.
(Dominica in Quinquagesima.)
Venite, convertimini ad me, dicit Dominus. Venite flentes, fundamus lacrymas ad Deum: quia nos negleximus, et propter nos terra patitur. Nos iniquitatem fecimus, et propter nos fundamenta commota sunt. Festinemus iram Dei antevertere, flentes, et dicentes: Qui tollis peccata mundi, miserere nobis.
Come, be converted unto me, saith the Lord. Let us come weeping, and pour out our tears before God, for we have been negligent, and because of us is the earth suffering. We have committed iniquity, and because of us are the foundations of the world moved. Let us hasten to avert the wrath of God; let us weep, and say: O thou, that takest away the sins of the world, have mercy upon us!
 Ps. ii 2.
 Ps. ii. 3.
 Ibid., 9.
 Ibid., 12.