Igor Markov's answer to Why does the US government spend so much on military? Jon Davis' answer to Given that China is fine without blue-water navy, why does the US need one? Being even is the Deadliest form of Warfare
Imho the most influential war in history is the Caesar Augustus' failing attempt to conquer the Germans. He sent two legions over the Limes Renano expecting to tame the german population. It didn't happened: in the Battle of Teutoburg Forest the army of 15.000 well trained roman solders was completely slayed but Germans. In a what if...
The Top Ten. 1 Stalingrad (World War II, 1942-43) Something ridiculous like 19 of the 20 most bloody battles in history took place on the Eastern Front in WW2 between Russia and Germany - Stalingrad was the one that knocked the stuffing out of the German War machine. The only 2 Battles that had as potentially as big an impact in History are the Battle of Britain and the Battle of Hastings.