Well there is the thesis of the "military revolution" first formulated by
Michael Roberts in the 1950's, not everyone agrees but in essence now real replacing critique has been founded as of yet, it has most deeply been expanded (with critique) upon by
Geoffrey Parker ;
http://www.spectacle.org/697/yee.html
In short: both Maurits and Gustaphe lay the foundations of modern warfare with modern (
land-cause the M.R. encomprises much more then just land combat)armies. For example Maurits introduced training in the winter (rather then disbanding most of the army and sending them home till the right season), he also took care of supplying his men with uniforms, so they'd look the same on the battlefield. Another member of the Nassau family printed drill books which quickly became standard. Gustaphe can write the same on his conto, though for more details I'd have to read in on it again, I'm basically writing down what I still remember of this subject. In short it comes down to this, when we talk about
the emergence of modern warfare we talk about the several evolutions that took place in this period: new technologies leading to new strategies and tactics, in other words: the military profession became more and more 'professional' and larger in scale. From now armies (and military infrastructure) became more and more expensive (for example the winter drill meant men were more trained but also more expensive and more valuable).
Scale enlargement (in a variety of field, not just land but also naval combat and siege warfare, see the short summary with the link above) and all that it encompasses might very well summon this up best. And when it comes to combat on land (so not siege warfare - for this happened earlier) Maurits and Gustaphe were what we would call pioneers;