An excellent place to start would be to review Noah Trudeau's article in the MHQ, "Prussia's American Observers." One of the things that has bothered me about the American Civil War and German Wars of Unification is that officers from both sides refused to accept that the other was an excellent example of the changing face of modern warfare. Justus Scheibert's memoir outlines several key elements that led to Moltke's victories, most notably the use of trains to move large bodies of troops and the support staff to work out the logistics of such a move. Furthermore, he and several lesser Prussian officers noted that cavalry were useful for recon and protecting the vanguard, but unless they were dismounted and equipped with repeating rifles or modern breech loaders, cavalry was useless on the modern field. (Obviously, this would be a lesson that was not widely accepted until much later.)

Bergeron's Confederate Mobile is an excellent source to see how Prussian engineers saw things. Major Von Sheliha was charged with organizing the forts and earthworks of Mobile, Alabama. Early on, von Sheliha noted that rifled artillery was superior to the brick and mortar forts the Federal government had constructed before the war. Even packing extra dirt and support bales didnt really help. If you look at the Siege of Paris, it seems that Moltke is working out the system used at Vicksburg, South Alabama, Richmond, and other places. Von Sheliha was more focused on constructing trench systems, setting torpedoes in the sea lanes, and moving defensive artillery to more secure locations. (He proposed creating a labor force of free-blacks who would be paid and fed like the white troops, but the Confederate government ignored him. Most of his plans were unfinished when Farragut arrived because the government failed to secure labor parties of enough men or men strong enough to endure the hard labor.) Von Schliha published a work after the war called A Treatise on Coast Defense which should be read alongside Mahan and some of Tirpitz's early ideas on fast attack ships, in my opinion. I should note that there is no "smoking gun" evidence Moltke used American Civil War strategies and tactics. His oft-used quote is rather ridiculous and I doubt he said it, but he never openly acknowledged the Americans.

To answer your question, Sheridan was not really justified but he had some legitimate arguments to make. Artillery use was something the Federal Army was constantly altering and to see that the German/Prussian system was perhaps nothing revolutionary led him to say this. Furthermore, as a cavalry commander, he was all too aware that a fast moving force with repeating/quick loading weapons was necessary. He also would have noted that an entrenched position was key in drawing an enemy out or keeping an enemy secure in a poor position. The railroad was also a necessity in moving men and material. If he looked at these things he probably saw the same issues he witnessed 5 years earlier in the Civil War. However, the Staff system implemented by Moltke was far superior to that of the Americas. The education of the Prussian officer corps was stronger than those who graduated from West Point. The system of war games that are still in use today are a product of Moltke's experimentation with his junior staff officers. These games were more important in the development of US Naval policy. (Something Sheridan could not have foreseen.) Finally, Moltke divided his forces into grand armies in ways that Grant dared not. The trust in his staff and the communication between the commander and the head of each army was so strong that the French were taken completely aback. Grant came close to this kind of movement, but his armies were never as large and never worked with such precision. See Bucholz's Moltke and the German Wars for more examples. Read some of Gary Gallagher's works on campaigns, like the Wilderness, to see some comparisons.

EDIT: Whoa! Thanks for the gold. I wrote an honors thesis on this topic some years ago. I do not know the most recent literature on the topic, however. Thanks again.

I am copy/pasting my response from the thread that likely originated this question.

I think Meade Sheridan was plain wrong in his assessment of Germany, and allowed his personal prejudices to cloud his judgement. The Prussian army used cavalry for recon, screening, raiding, and protecting supply trains. Sheridan thought it would be better utilized in a more traditional role of shock cavalry and post-engagement sweeping maneuvers to destroy broken units. He nearly came to blows with his commanding officer, Meade, over the use of cavalry in the American Civil War.

The Prussian Army in 1871 was highly modern. Each soldier had a long range accurate bolt action rifle called a needle gun. It could put 10-15 aimed shots down field with an accurate range up to 600 meters. Compare this to the Springfield Musket which could put 2-4 shots per minute, accurate up to 200 meters. Combine this with the Krupp 6lb cannon which had a lightning fast rate of highly accurate and deadly fire, and early machine guns, and I am forced to conclude that offensive cavalry would have been as pointless as it was in World War I.

I am in line with Yawarpoma and I'd like to add something. Ex military here with a lot of military history on my shoulders. One of the things I noticed from the historical texts is the lack of ability of the authors to "re-situate" themselves when in a different context. Sheridan grew militarily in the American West until the coming of the Civil War, mainly in Texas and California. The tactical procedures required in these territories have no parallel in Western/Central Europe. Similarly the Civil War that would see him raise to General Officer and future head of the US Army had many differences with wars in the European continent, yet Sherman prevailed and rose in the Civil War which, in my view, could only reinforce the fact that the Union and his small group of elite commanders were perfectly right. I saw Sheridan's comments years ago and my initial reaction was that of "what a petulant guy, sure something in Europe was worth to look into" but after much studying I came to believe that he was truly honest but just from his tactical (and strategical by now) perspective. European armies offered nothing relevant for the tactical and strategical context in which Sherman had to maneuver. US landscapes and a low intensity war with the Indians that Sherman took on few days before the end of the Civil War did not need what Europe had to offer. Probably colonial war in India or Africa offered a more interesting field for him that continental Europe. After all Sherman was an observer that should bring back home anything the US could benefit from, in this case may be nothing since the Civil War was over and the US would not think in terms of aggressive neighbors nor get involved in international warfare for many decades.