"The Caliphate is based upon the Annals of Ibn-al-Athir, a singularly impartial annalist, who lived and wrote at Mosul in the early part of the thirteenth century A.D. Ibn al-Athir's work is an epitome and continuation of that of the much older historian Tabari.
Sir William Muir's The Caliphate and life of Mohammad are works of classical value and leave one with a strong impression of the author's extreme accuracy in reproducing the statements of his authorities, as well as of the soundness of his judgement in weighing the evidence in support of the accounts.
The value of Tabari's work, again, lies in the fact that it consists almost wholly of citations from much older sources, some of which are nearly contemporary with the events recorded. All of these lived under the 'Abbasid dynasty, yet this fact does not appear to have prejudiced their results so much as one might expect. The Umeiyads are not, upon the whole, painted in much blacker colours than the 'Abbasids, nor are the defects of the latter suppressed. The worst feature of all, from our point of view, their in human cruelty and disregard of life, is common to both. It is generally upon theological grounds that the Caliphs are acquitted or condemned; and the pictures of them which have come down to us are free from caricature and apparently true and fair.
Arabic history tends to be almost entirely anecdotal in character, and this no doubt helps one to picture to oneself the figures on the screen and the times in which they moved. It is necessary, however, also to take account of the forces which shaped and governed the events. Sir William Muir has given full weight to one of the most powerful of these, the perennial jealousy of the Northern and Southern Arabian tribes; but this done in much more detail in Wellhausen's Das Arabische Reich and Sein Sturz, and many of his observations have been incorporated in the present edition. Chapter fifty eight on the rival fortunes of the clans in Khorasan is drawn entirely from this work. Persons and events thus become connected together in the way of cause and effect; and the reader runs less risk of not seeing the wood for the trees."