_Two Impulses, the Intellectual and Moral, operating against the
Mediaeval state of Things.--Downfall of the Italian System through the
intellectual Impulse from the West and the moral from the North.--Action
of the former through Astronomy.--Origin of the moral Impulse.--Their
conjoint irresistible Effect.--Discovery of the state of Affairs in
Italy.--The Writings of Machiavelli.--What the Church had actually
done._

_Entire Movement of the Italian System determined from a consideration
of the four Revolts against it._

[Sidenote: The Eastern pressure.] From the West I have now to return to
the East, and to describe the pressure made by Mohammedanism on that
side. It is illustrated by many great events, but, above all, by the
fall of Constantinople. The Greek Church, so long out of sight that it
is perhaps almost forgotten by the reader, comes for a moment before us
like a spectre from the dead.

[Sidenote: Invasions of the Turks.] A wandering tribe of Turks had found
its way into Asia Minor, and, under its leader Ertogrul and his son
Othman, consolidated its power and commenced extending its influence by
possessions taken from the sultans of Iconium and the Byzantine empire.
The third prince of the race instituted the Janissaries, a remarkable
military force, and commenced driving the Greeks out of Asia Minor. His
son Soliman crossed the Hellespont and captured Gallipoli, thus securing
a foothold in Europe, A.D. 1358.

[Sidenote: Extension of their power in Europe.] This accomplished, the
Turkish influence began to extend rapidly. Thrace, Macedon, and Servia
were subdued. Sigismund, the King of Hungary, was overthrown at the
battle of Nicopolis by Bajazet. Southern Greece, the countries along the
Danube, submitted, and Constantinople would have fallen had it not been
for the unexpected irruption of Tamerlane, who defeated Bajazet and took
him prisoner. The reign of Mohammed I., who succeeded, was occupied in
the restoration of Turkish affairs. Under Amurath II., the possession of
the Euxine shore was obtained, the fortifications across the Isthmus of
Corinth were stormed, and the Peloponnesus entered.

[Sidenote: The Byzantine sovereigns apply to the West.] Mohammed II.
became the Sultan of the Turks A.D. 1451. From the moment of his
accession, he turned all his powers to the capture of Constantinople.
Its sovereigns had long foreseen the inevitable event, and had made
repeated attempts to secure military aid