From: THE RT. HON. SIR WINSTON CHURCHILL K.G., O.M., C.H. GREAT DESTINY. Sixty years of the memorable events in the life of the man of the century recounted in his own incomparable words. Edited by F. W. Heath. G. P. PUTNAM’S SONS NEW YORK 1962, 1965 BY ODHAMS PRESS LIMITED, LONDON. FIRST AMERICAN EDITION, 1965. pp. 388-389; (Hat tip Roy Bishko)
In the middle of April  the Germans took a sombre decision. [General] Ludendorff refers to it with bated breath. Full allowance must be made for the desperate stakes to which the German war leaders were already committed. They were in the mood which had opened unlimited submarine warfare with the certainty of bringing the United States into the war against them. Upon the Western front they had from the beginning used the most terrible means of offense at their disposal. They had employed poison gas on the largest scale and had invented the “Flammenwerfer.” Nevertheless it was with a sense of awe that they turned upon Russia the most grisly of all weapons. They transported Lenin in a sealed truck like a plague bacillus from Switzerland into Russia. Lenin arrived at Petrograd on 16 April. Who was this being in whom there resided these dire potentialities?
Lenin was to Karl Marx what Omar [Caliph Umar] was to Mahomet [Muhammad]. He translated faith into acts. He devised the practical methods by which the Marxian theories could be applied in his own time. He invented the Communist plan of campaign. He issued the orders, he prescribed the watchwords, he gave the signal and he led the attack.
From my Iran’s Final Solution For Israel, pp. 106-107:
Alfred von Kremer, the great 19th century German scholar of Islam, described the “central idea” of Umar’s regime, as being the furtherance of “…the religious-military development of Islam at the expense of the conquered nations.” The predictable and historically verifiable consequence of this guiding principle was a legacy of harsh inequality, intolerance, and injustice towards non-Muslims observed by von Kremer in 1868 (and still evident in Islamic societies to this day, nearly 150 years later):
It was the basis of its severe directives regarding Christians and those of other faiths, that they be reduced to the status of pariahs, forbidden from having anything in common with the ruling nation; it was even the basis for his decision to purify the Arabian Peninsula of the unbelievers, when he presented all the inhabitants of the peninsula who had not yet accepted Islam with the choice: to emigrate or deny the religion of their ancestors. The industrious and wealthy Christians of Najran, who maintained their Christian faith, emigrated as a result of this decision from the peninsula, to the land of the Euphrates, and ‘Umar also deported the Jews of Khaybar. In this way ‘Umar based that fanatical and intolerant approach that was an essential characteristic of Islam, now extant for over a thousand years, until this day [i.e., written in 1868]. It was this spirit, a severe and steely one, that incorporated scorn and contempt for the non-Muslims, that was characteristic of ‘Umar, and instilled by ‘Umar into Islam; this spirit continued for many centuries, to be Islam’s driving force and vital principle….With a strong hand, he held the reins of spiritual and worldly power, commanded with unlimited full authority over the political and religious activities of Muslims, already many millions in number. Under him, the conquest of Syria was completed, Iraq and Persia were conquered as far as the Oxus and the borders of Hindustan, while in the west, Egypt obeyed him…
The jihad campaigns waged in the era of Umar’s Caliphate, consistent with nascent Islamic Law (Sharia), spared neither cities nor monasteries if they resisted. Accordingly, when the Greek garrison of Gaza refused to submit and convert to Islam, all were put to death. In the year 640, sixty Greek soldiers who refused to apostatize became martyrs, while in the same year (i.e., 638) that Caesarea, Tripolis and Tyre fell to the Muslims, hundreds of thousands of Christians converted to Islam, predominantly out of fear.
Muslim and non-Muslim sources record that Umar’s soldiers were allowed to break crosses on the heads of Christians during processions and religious litanies, and were permitted, if not encouraged, to tear down newly erected churches and to punish Christians for trivial reasons. Moreover, Umar forbade the employment of Christians in public offices.
The false claims of Islamic toleration during this prototype “rightly guided” Caliphate cannot be substantiated even by relying on the (apocryphal?) “pact” of Umar (Ibn al-Khattab) because this putative decree compelled the Christians (and other non-Muslims) to fulfill self-destructive obligations, including: the prohibition on erecting any new churches, monasteries, or hermitages; and not being allowed to repair any ecclesiastical institutions that fell into ruin, nor to rebuild those that were situated in the Muslim quarters of a town. Muslim traditionists and early historians (such as al-Baladhuri) further maintain that Umar expelled the Jews of the Khaybar oasis, and similarly deported Christians (from Najran) who refused to apostasize and embrace Islam, fulfilling the death bed admonition of Muhammad who purportedly stated: “there shall not remain two religions in the land of Arabia.”
Umar imposed limitations upon the non-Muslims aimed at their ultimate destruction by attrition, and he introduced fanatical elements into Islamic culture that became characteristic of the Caliphates which succeeded his. For example, according to the chronicle of the Muslim historian Ibn al-Atham (d. 926-27), under the brief Caliphate of Ali b. Abi Talib (656-61), when one group of apostates in Yemen (Sanaa) adopted Judaism after becoming Muslims, “He [Ali] killed them and burned them with fire after the killing.” Indeed, the complete absence of freedom of conscience in these early Islamic Caliphates— while entirely consistent with mid-7th century mores—has remained a constant, ignominious legacy throughout Islamic history, to this day.