The general gist I hear about WW1 was that it was a complete culture shock to all the countries fighting in it regarding how it was going to be fought, as though armies and soldiers were still expecting to march in lines on pitch battlefields. This lack of experience in the new era of modern war therefore leading to massive casualty numbers.
In complete hindsight, are there any wars or battles before WW1 with enough hints and signs where one could deduce that battles were about to significantly change and traditional standards of battle were becoming more archaic if not outright suicidal?
Like someone trying to warn generals before the war that these new machine guns were actually extremely deadly and we should start building counters (tanks?) sooner rather than later?
In complete hindsight the American Civil war, the Crimean war, Russo-Japanese war, and Franco Prussian war can all serve as warnings for WW1 to one extent or another.
The American civil war showed the folly of massed frontal attacks against a fortified position. The weapons of the period extracted a huge toll due to the tactics used at the time. Trench warfare also featured heavily during the ground war. In the war at sea we see the importance of a naval blockade with the aim of starving out your oponents industry if not their people. The Union navy had great sucess during their blockades while the Confederate navy adopted commerce raiding and blockade running. An uncanny comparison to the situation of the British and German empires during the war. The war was also very much an industrialized war where the individual skill of a soldier affected the outcome of a battle less than which side had more guns and munitions to throw at their enemy. The war also saw the first use of a torpedo in a submarine to sink a ship, while not the torpedos we are used to its still a revolutionary first step.
During the Crimean war, trench warfare was used extensively during the siege of Sevastopol. Here the allies learned of the great deal of health problems that comes with trench warfare from its facilitation of plagues to its own breed of fun deseases like trench foot. The allies also experienced their first amphibious operations against a peer enemy in the industrial era and all the logistical problems that brings with it. Sinchrinized assaults on trench lines were also featured during the war thanks to the first use of sinchronized watches. In general the crimen war bread a certain type of misery in the battlefield very much akin to ww1 more so than trench warfare during the Civil War even.
The Franco Prussian war tought the vital importance of logistics during an industrial war. Not only in the sense of arms but in speed of mobilization. With a good logistical infrastructure you could quite litteraly dictate the course of the war as the enemy would be forced to respond to your faster military response. Artillery while featuring heavily during the American civil war and the crimean war, was very much the king of battle during the Franco Prussian war. Constant artillery strikes could be done against an enemy in open battle not only during sieges as it was more common previously. The range of artillery had also increased a fair deal than the pieces used during the American civil war and crimean war. The importance of a long yet mutually supporting frontline was also seen here for the first time. No longer was the front line a line on a map with entire armies maneuvering to bring each other into battle. The front line was a very real thing and all you needed to do to engage your enemy was push into their lines. While the war remained mobile even seeing the last great calvary clashes in European history, both sides came up against modern fortifications and suffered because of them. Already hastily built field fortifications had extracted a great toll on soldiers during the Crimean and American civil wars but the modern fortresses of this era were more capable still, instilling in the french at least the need for fortifications that they would continue to hold until the eve of ww2.
The Russo-Japanese war is closest to ww1 in literal terms as it was fought barely a decade before ww1. Both Russian and Japanese armies used trench warfare extensively, it took a heavy toll on both sides. Fighting was bloody and left the men with real sense of progress even when victory was achieved. There was very much a sense of stalemate due to the slow progress of trench warfare during its ground battles. While at sea the debut of predreadnought battleships fighting in large scale for the first time in history was very interesting to the other world powers. The deadlines of naval mines, fear of modern torpedo boats, importance of naval comunications when in battle, the importance of far flung naval bases with a heslthy amount of auxilary ships and more were all in full display. The world was still learning how to use sea power effectively and they tool notice to the faliures of the Russian navy and the sucess of the Japanese navy. Overall there was a general drive by most powers to compete in a naval arms race for a decade before the war but the war cemented the importance of such efforts in future conflicts.
As to what should they have built before the war varies depending on the nation. Overall a good railway system for troop and materiel transportation, decent forts at vital points, the importance of naval infrastructure and a navy in general. Those seem to be prudent lessons to be learned from these wars as to offensive tactics the combined arms approach of artillery with infantry was also prudent. The lesssons of ww1 sadly could only be taught by experiencing industrialized total war.