Liddell Hart was pretty damned influential as both a historian and a military theorist. It's probably an exaggeration to credit him, J.F.C. Fuller, Charles de Gaulle and Heinz Guderian with creating modern maneuver warfare, but the thinking of all certainly played a role. I'm pretty sure I read The German Generals Talk as far back as high school, but I've also read several other works of his. He and the other maneuver warfare theorists enjoyed a resurgence in the 1970s/80s as the U.S. Army went through a fundamental reassessment of how it approached warfare.
I too can see a lot of lessons from the U.S. Civil War as influencing later doctrinal developments in Europe. To what you observe about Sherman, I'd also add the use of railways to facilitate not just logistics but also maneuver by allowing forces to operate on exterior lines and converge on a decisive point. More ominously, of course, the experience of trench warfare in the Richmond/Petersburg campaign might be seen as presaging World War I.
On the flip side, a few years ago I read a dissertation from the School of Advanced Military Studies at the Command & General Staff College by a Bundeswehr officer. He argued that European, especially German, military observers took few lessons from the US Civil War. To the extent European thinkers took lessons on these matters, it was mainly more from their own experiences in Crimea, the Austro-Prussian War, the Franco-Prussian War, etc.
I am not sure if I completely agree with his thesis; I think European observers took lessons from the U.S. experience, even if they only reinforced lessons from their own conflicts. There was a tendency for Europeans to dismiss Americans as lacking their level of military organizational and technological sophistication, as well as to claim that the terrain, population density, etc. of the U.S. was too different from Europe to allow for application of U.S. experience. However, I've read Moltke the Elder's own writings from his service as an advisor to the Ottoman army during the Egyptian–Ottoman War. Despite the obvious differences in terrain and technology between the Ottoman Empire in 1839 and central and western Europe in 1866 and 1870-71, there's a clear through-line between Moltke's observations then and the lessons he put into practice as Chief of the General Staff.
