Defence through the ages

Historically, it was generally true that defenders had an advantage over attackers. Battles commonly focused on seiges important cities, allowing defenders to strengthen their position. They had the ability to make preparations for the battle to protect themselves from the enemy while making the enemy vulnerable, e.g. preparing positions such as trenches and fortification or in more recent times laying obstacles such as land mines and tank traps. However in encounters larger than the small scale the attacker may often have the advantage, since they get to choose the time and place of battle. An attacker may concentrate their entire force on a small part of the defended area, while the defender is forced to spread their forces over the possible area of attack.

In the modern era the defenders' advantage has been gradually reduced, due to factors like the increased mobility of the modern forces, better communication technology and increased destructiveness of weaponry - reinforced underground bunkers which would previously have been unassailable can be eliminated instantly by bunkerbuster missiles or tactical nuclear weapons