Sometimes the most important items are of necessity omitted.

But the information which they contain is enormous; and, seeing that the rules of the public service keep the original records in Great Britain closed for well-nigh a century, only the most fastidious can object to the use of the wealth of materials given to the world in _Parliamentary Papers_.
Besides these published sources there is the fund of information possessed by public men and the "well-informed" of various grades.
Unfortunately this is rarely accessible, or only under conventional restrictions.

Here and there I have been able to make use of it without any breach of trust; and to those who have enlightened my darkness I am very grateful.

The illumination, I know, is only partial; but I hope that its effect, in respect to the twilight of diplomacy, may be compared to that of the Aurora Borealis lights.
After working at my subject for some time, I found it desirable to limit it to events which had a distinctly formative influence on the development of European States.

On questions of motive and policy I have generally refrained from expressing a decided verdict, seeing that these are always the most difficult to probe; and facile dogmatism on them is better fitted to omniscient leaderettes than to the pages of an historical work.