Such as the Battle of Gettysburg where the Confederate States lost a large portion of their army and were decisively put on their back foot, or another example in the American Civil War with General Sherman’s March to the Sea where Sherman basically marched unsupported through enemy territory and to the Atlantic. In modern times, he would have been surrounded and his force destroyed but in the Civil War that didn’t happen.
Another example is how small states like Poland and Prussia and France were able to defeat or destroy the armies of much larger states such as Russia, Austria , and Russia again.
The armies of both sides met and destroyed each other in one or two decisive battles even though they didn’t seem to need to necessarily do that. This kind of fighting allowed small states to defeat large ones in one battle and win a war.
In modern times, this style of fighting is completely useless as one large army can be surrounded by many smaller units staffing a large and continuous front line with consistent battles and skirmishes along the way. Why weren’t these strategies used to defeat large armies in the past?
Sorry for any formatting or spelling errors, I’m on mobile.
Someone else will probably be able to give you a better sourced answer, but here we go.
The short answer is that it was simply impossible to pull off before the end of the 19th century. So, the approximate period when this happened is the end of the 19th century and the first half of the 20th century.
The doctrinal changes were enabled by advances in technology.
It's all about command and control. Battles are not quiet affairs and you need a way to issue orders to the troops. In the middle of a battle it's difficult. You need to delegate, use messengers or develop ways of signalling orders. This seriously limits the distance you can really command from, rendering long-range coordination required by continuous front lines to actually work impossible. It's pretty much impossible to effectively command when communications lag is too high - if it takes a day for a messenger to reach the command, they're pretty much on their own, as it would also take a day for any response to arrive - which is plenty of time for the fighting to be pretty much over. Even it the time it takes for information to flow is on the order of hours, it might be too long. This is without considering the possibility that the messenger might be captured or killed on the way.
While the telegraph started showing up in the 19th century, radio and telephone appeared only towards its end. Obviously, it took a while to adopt them and figure out a way to employ them militarily, but by the time the Great War started, they were utilised to coordinate forces on a scale previously unprecedented. Now, the speed at which the information can flow is crucial and David French's Raising Churchill's Army clearly shows the concepts being perfected as the British Army improved the flow of orders through communication technology over the war. It's no coincidence: instant communication allows the scout reports to be fresh and the orders to arrive soon enough to be acted on over hundreds of kilometres. It's possible to send in reserves as the clash starts, and so there's no need to immediately mass the troops in one place. Obviously, I extrapolate a little, but as French shows in the book, improvements in communication were crucial. French actually points out how such a simple thing as radio availability could multiply combat capabilities. Without telephone and radios, these tactics and strategies were outright impossible to pull off, since they rely on instant communication at their core.
The aim of a war is to meet a certain goal. Usually it means forcing the enemy to yield to some demands. This means a need to break armed resistance. Now, quantity is a quality of its own and, in fact, even modern doctrines do rely on concentrating forces efficiently. But when you don't have sufficiently fast long-ranged communications, you need to concentrate your forces in an army, and big battles in the field allow manoeuvre and so on. Scouts need to reach the area and report back, the runners need to deliver movement orders, and so on. This slower communication also means that the results of a battle are not immediately dispersed, along with many other implications. But it breaks down to the fact that for a supreme commander there's only one viable option: massing troops and sending them somewhere to break the enemy. Since they can't let the force keep pillaging or take forts unopposed, they need to meet them in battle. And once an army without modern communications breaks, it's a titanic endavour to put it together, nevermind the morale impact.
Just look at the Boer War: it was before the First World War and showed the British that they needed to adjust in the face of highly-mobile combat. Then, the Great War utilised the communications technology so widely it was clearly indispensable. WW2 further proved the importance of radios and largely spelled doom for the decisive battle.
Note that I sort of ignored the massive growth in industrial capability in that period. The question actually ties into industrial capabilities and general logistics. This was, in fact, sped by instant communication as well, as it was now much easier to organise production - without it, it was harder to optimise the required supply chains on such a massive scale. As the telegraph and telephone lowered the economic risks involved in mass production which was necessary to supply the armies, they pretty much enabled them to reach the scale needed.
Of course, even if we were to assume it was possible to produce enough materiel to support the large forces required for this kind of warfare in the first place, the lack of instant communication would make it impossible to command or supply them as needed, anyway.
Source:
Raising Churchill's Army: the British Army and the War against Germany, 1919-45
David French
Oxford, Oxford University Press, 2000