Hi FTS,
I could readily understand the American Civil War being a turning-point in warfare.
However, World War One was he first time in which modern industrialised countries went to war with one another.
Although the North had some industry, the USA of 1861 was still largely an agricultural country. (That all changed rapidly during the following decades, of course. For example, by 1890, the USA was producing more steel than anybody else).
Likewise during the Franco-Prussian War of 1870. While Prussian technology largely won the day at the decisive Battle of Sedan, Germany's industrialisation took place after its unification. (e.g. regarding Bismarck's famous "Blut und Eisen" speech, many commentators have remarked that it should have been more accurately rendered "Coal and Iron"!).
Even during the South African War of 1899-1902, the two Boer republics were agricultural countries, even bordering on frontier societies (albeit financed by the gold mines of the Witwatersrand).
By 1914, though, at least three of the belligerents - Britain, France and Germany - were industrial countries. To that extent, WWI was the first time industrialised countries fought each other in all out warfare (rather than by selling their weapons to another party to fight on their behalf!)