To appreciate the tale, it will be necessary to have a clear idea
of the state of affairs in Europe at the time. The war which was
convulsing Germany, and in which almost every other European power
interfered at some time, was the Thirty Years' War (1618--1648), a
struggle having a special character of its own as the last of the
religious wars which had torn Europe asunder for a century and the
first of a long series of wars in which the new and purely political
principle of the Balance of Power can be seen at work. The struggle
was, nominally, between Protestant and Catholic Germany for, during
the Reformation period, Germany, which consisted of numerous states
under the headship of the Emperor, had split into two great camps. The
Northern states had become Protestant under their Protestant princes.
The Southern states had remained, for the most part, Catholic or had
been won back to Catholicism in the religious reaction known as the
Counter-Reformation. As the Catholic movement spread, under a Catholic
Emperor like Ferdinand of Styria, who was elected in 1619, it was
inevitable that the privileges granted to Protestants should be
curtailed. They determined to resist and, as the Emperor had the
support of Spain, the Protestant Union found it necessary to call in
help from outside. Thus it was that the other European powers came to
interfere in German affairs. Some helped the Protestants from motives
of religion, more still from considerations of policy, and the long
struggle of thirty years may be divided into marked periods in which
one power after another, Denmark, Sweden, France, allied themselves
with the Protestants against the Emperor. The _Memoirs_ are
concerned with the first two years of the Swedish period of the war
(1630--1634), during which Gustavus Adolphus almost won victory
for the Protestants who were, however, to lose the advantage of his
brilliant generalship through his death at the battle of Lützen in