Tactics/Leadership, without a doubt. I can't really separate the two as they are too closely interrelated.
The most well armed army in the world can be destroyed by a group of archaic armed savages if the savages have a large enough benifit in leadership and tactics. Have an utter lacking in leadership and tactics and you will never win in the long run. Even your victories will be losses because they will be prohibitively expensive ones.
THis has been proven time and again.
All the factors are important but leadership/tactics are the key. Without them nothing else matters nearly as much.
If this is the case then why did the South lose the Civil War? Why did the Germs lose WWII?
Modern wars (since 1860) are principally won by industrial power, also by weight of population, which is usually related to industrial power. This is why the North beat the South (despite mostly inferior leadership), and why the Allies beat the Germans in both World Wars. Vietnam was an exception, mostly because the Americans lacked the political will to bring their full might to the war.
Upvote
0