Here, here! What tends to get forgotten is that the lessons of the War of Northern Agression were there for all to see, including European military observers. They were cast aside as irrelevant, because those American bumpkins didn't know how to fight a war. It took the War to End All Wars to make Europe understand the lessons that we had already painfully learned.
Next time I meet you, I will have to remember to say Seig Heil.
You are quite correct. However, the Europeans had the unfortunate experience of winning all these colonial wars during the 19th century, using breech-loading rifles and machine guns against natives armed with swords, spears and bows.
Each nation decided that their ability to defeat native armies that outnumbered them dramatically was a consequence of their own magnificent military capability. They each then tried to do the same in 1914 up against other Europeans armed and trained in the same way. Didn't work.
BTW, the Europeans could have learned not only from our Civil War, but also from the various Italian and German wars of unification. But those wars were generally too short for anybody to draw the obvious conclusions. The Brits also got their tail in a crack against the Boers, but nobody applied the lesson.
To be perfectly fair, the defensive grew more and more powerful up to 1917. Only the development of tanks, and of German storm tactics, were finally able to restart effective offensives.
We can criticize the generals of 1915 and 16 all we want, but there was no real solution to their dilemma at the time. Not attacking just left their troops in the trenches, gradually being destroyed by artillery. Any general who refused to attack would just be removed by politicians and replaced by a general who told the politicos what they wanted to hear, that he could win the war.