Even more specifically were there any battles that showed the old methods of warfare needed to be drastically and immediately changed?
These previous answers should be pertinent.
As the 17th century was the time of such conflicts as the French Wars of Religion, The Wars of the Three Kingdoms on the British Isles, the Thirty Years War, and the latter part of the Eighty Years War, I would strongly hesitate to call the warfare of that period in European "gentlemanly". Warfare in the 18th century and 19th century was complex, although there is a tendency to depict it as a gentlemanly clash, two sides lining up on a field and shooting at each other in pitched battles. I'll leave it to the early modern military history experts to dissect, but raids, sieges, and bloody battles such as Malplaquet, Borodino and Waterloo were far from gentlemanly, and things such as line formations were designed to allow volley fire (muskets were inaccurate beyond 50 yards) and maintain unit cohesion, though skirmish formations and dedicated skirmishers like Jagers, and Voltigeurs were present. In North America, British, French, Spanish and American forces engaged in war fighting that involved sieges, pitched battles and often vicious raiding with irregular forces.
As to how "this" method of war changed, I'd recommend here Nicholas Murray's excellent book The Rocky Road to the Great War: The Evolution of Trench Warfare to 1914, or you can watch his lecture [here] (https://www.youtube.com/watch?v=2cbq7iu8FrI). Starting in the 1830s and 40s, and gaining speed with the 1850s and 60s, the spread of industrialization spurred important developments in European ways of war. By the 1850s, round ball and conical minie ball rifled muskets, largely percussion capped, were entering widespread service and increasing the effective range, reliability, and rate of fire of infantry longarms. At the same time, cannons became rifled like the La Hitte system in France, increasing the range, accuracy, and velocity of artillery fire. By the 1860s and 70s, breech-loading rifles and artillery pieces were entering service, the Prussians having adopted the Dreyse Needle Rifle in 1849, and entering the Franco-Prussian War with a formidable artillery train of breech-loading guns. Railways proliferated, enabling swift supply of armies as well as their movement over great distances, while steady improvements in quality of life and the growth of European nationalism furnished Great Powers with armies hundreds of thousands strong, even larger than the armies of Napoleon.
In turn, the way battles were conducted changed. A. J. Ecchevaria and especially Stephen Badsey, have written about the revival of the European mounted arm at this time after the firepower revolution appeared to have placed them in doubt (Badsey's [thesis] (https://www.repository.cam.ac.uk/bitstream/handle/1810/244878/Badsey12201.pdf?sequence=1&isAllowed=y) is excellent for covering the controversy). Cavalry was now to be highly trained, kept in large corps and divisions when the armies clashed but dispersed to scout and reconnoitre when on the march, and idealy should be capable of dismounted "fire" and mounted "shock" action, the epitome of this being the British Cavalry in WWI.
With infantry and artillery, conflicts like the Russo-Japanese War indicated the importance of indirect fire, and the Second Anglo-Boer War saw the use of massed barrage fire by the Royal Artillery on a significant scale. Heavy Siege artillery, like howitzers and mortars, entered arsenals in the 1880s and 90s in recognition of the difficulty posed by modern field fortifications and permanent fortifications. Infantry were to advance on the battlefield in dispersed groups, akin to skirmish lines, and always under the cover of artillery and eventually machine gun fire. Cavalry was no different, charging in loose formation after the enemy's positions were brought under fire. Artillery continued to evolve, with hydraulic or pneumatic recoil systens enabling greater accuracy and fearsome rates of fire (15 75mm rounds per minute for the French Mle 1897).
In response to the firepower revolution, field fortifications took on greater importance. German training manuals in 1906 devoted 20 pages to defensive fighting, compared to 6 in the 1880s, and Russian infantry were trained to dig-in on the battlefield, in light of the Russo-Japanese War. There was a shift, noticeably, away from above ground redoubts, breastworks and other forms of cover that proliferated notably in the Civil War (thus not proper Trench Warfare per se), and towards below ground (subterranean as it were) fortifications, that kept soldiers out of the sight of the enemy and sheltered from the worst fire.
Above all, European military thinkers knew the immense strain on the soldier that the modern battle would place. He would not be in close order as in Napoleon's time, but spread out and quite 'naked' with the tremendous firepower to be called upon both to stop an advance and to allow it to take place! As a result, thing like elan, esprit de corps, the 'Offensive Spirit' etc were emphasized alongside training and drill, by officers like Foch, Grandmaison and others, to ensure that a soldier would be able to function on the battlefield.
All of these developments played out, not always as intended or effectively, in France and Flanders from August to November 1914. The result of huge armies, with immense firepower and equally immense logistical problems and casualties by the year's end, was that all the armies dug-in in field fortifications, as a matter of practice for the British and French, as well as necessity for the Germans. Thus creating the Western Front.
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