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 Battle of Hastings is generally accepted as the earliest big battle of the Middle Ages. On Saturday 14th October 1066 the general of the invading French forces, Duke William of Normandy (Also known as William the Conqueror) and King Harold Godwinsson battled on the green pastures of Hastings.