The great thing was to bring the whole broadside force to bear on an enemy.  Whether this was to be impartially distributed throughout the hostile line or concentrated on one part of it depended on the character of particular admirals.  It would have been strange if a period so long and so rich in incidents had afforded no materials for forming a judgment on the real significance of sea-power.  The text, so to speak, chosen by Mahan is that, notwithstanding the changes wrought in naval materiel during the last half-century, we can find in the history of the past instructive illustrations of the general principles of maritime war.  These illustrations will prove of value not only ’in those wider operations which embrace a whole theatre of war,’ but also, if rightly applied, ’in the tactical use of the ships and weapons’ of our own day.  By a remarkable coincidence the same doctrine was being preached at the same time and quite independently by the late Vice-Admiral Philip Colomb in his work on ‘Naval Warfare.’  As a prelude to the second Dutch war we find a repetition of a process which had been adopted somewhat earlier.  That was the permanent conquest of trans-oceanic territory.  Until the seventeenth century had well begun, naval, or combined naval and military, operations against the distant possessions of an enemy had been practically restricted to raiding or plundering attacks on commercial centres.  The Portuguese territory in South America having come under Spanish dominion in consequence of the annexation of Portugal to Spain, the Dutch—­as the power of the latter country declined—­attempted to reduce part of that territory into permanent possession.  This improvement on the practice of Drake and others was soon seen to be a game at which more than one could play.  An expedition sent by Cromwell to the West Indies seized the Spanish island of Jamaica, which has remained in the hands of its conquerors to this day.  In 1664 an English force occupied the Dutch North American settlements on the Hudson.  Though the dispossessed rulers were not quite in a position to throw stones at sinners, this was rather a raid than an operation of recognised warfare, because it preceded the formal outbreak of hostilities.  The conquered territory remained in English hands for more than a century, and thus testified to the efficacy of a sea-power which Europe had scarcely begun to recognise.  Neither the second nor the third Dutch war can be counted amongst the occurrences to which Englishmen may look back with unalloyed satisfaction; but they, unquestionably, disclosed some interesting manifestations of sea-power.  Much indignation has been expressed concerning the corruption and inefficiency of the English Government of the day, and its failure to take proper measures for keeping up the navy as it should have been kept up.  Some, perhaps a good deal, of this indignation was deserved; but it would have been nearly as well deserved by every other government