The general purport of these three missions of Cromwell in 1657 requires explanation.  Not commercial interests merely, but also zeal for union among the Protestant Powers, had all along moved his diplomacy; and now the state of things in the north of Europe was so extraordinary that, on the one hand, the cause of Protestant union seemed in fatal peril, but, on the other hand, if it could be retrieved, it might be retrieved perhaps in a definite and magnificent form.  The prime agency in bringing about this state of things had been the vast energy of the young Swedish King, Charles X. or Karl-Gustav.  Cromwell had by this time contracted an especial admiration of this prince, and had begun to regard him as a kindred spirit and the armed champion of Continental Protestantism.  To see him succeed to the last in his Polish enterprise, and then turn himself against Austria and her Roman Catholic clientage in the Empire, had come to be Cromwell’s desire and the desire in Great Britain generally.  For a time that had seemed probable.  In the great Battle of Warsaw, fought July 28-30, 1656, Charles-Gustavus and his ally the Elector of Brandenburg routed the Poles disastrously; and, Ragotski, Prince of Transylvania, also abetting and assisting the Swede, “actum jam videbatur de Polonia” as an old annalist says:  “it seemed then all over with Poland.”  But a medley of powers, for diverse reasons and interests, had been combining themselves for the salvation of Poland, or at least for driving back the Swede to his own side of the Baltic.  Not merely the Austrians and the German Catholic princes were in this combination, but also the Muscovites or Russians, and, most unnatural of all, the Danes, with countenance even from the more distant Dutch.  Nay, the prudent Elector of Brandenburg, hitherto the ally of the Swede, was drawn off from that alliance.  This was done by a treaty, dated Nov. 10, 1656, by which the Polish King, John Casimir, yielded to the Elector the full sovereignty of Ducal Prussia or East Prussia, till then held by the Elector only by a tenure of homage to the Polish Crown.  All being ready, the Danish King, Frederick III., gave the signal by declaring war against Sweden and invading part of the Swedish territories.  When the news reached Cromwell, which it did Aug. 13, 1657, it affected him profoundly.  He had previously been remonstrating, as we have seen, both with the Danes and the Dutch, by letters of Milton’s composition (ante pp. 272-3 and 290), trying to avert such an unseemly Protestant intervention in arrest of the Swedish King’s career.  And now, having his two envoys, MEADOWS and JEPHSON, ready for the emergency, he despatched them at once to the scene of that new Swedish-Danish war in which what had hitherto been the Swedish-Polish war was to be at once engulphed.  For Karl-Gustav had turned back out of Poland to deal directly with the Danes, and the interest was now concentrated on the struggle between these two powers—­the Poles, the