An attack always needs the same advantages to be succesfull,

A. Surprise
B. Numbers
C. Leadership
D. Will

The defender's job is to negate these advantages to overcome.

A. An answer to surprise is a planned defense.
B. Numbers can be counted with superior technology (ie Machine Guns), support (ie Flank attacks, artillery) or simply more numbers to slug it out (ie WW1)
C. This is a hard one to counter, it depends on how the defensive leadership handles the situation (ie El Alamein)
D. To counter attacking will, you need to strike morale, this is normally done by beating off attacks, and striking them where it hurts (ie Guerrila Warfare)

1) Vietnam War.

2) Battle of Hastings.

3) Battle of Agincourt.

4) Soviet Invasion of Afghanistan

5) Battle of Stalingrad

6) American Revolutionary War
1. Vietnam showed that if you can take away the 4 advantages, even lower tech soldiers can defeat a powerful nation. North Vietnam knew by invading the South they would be facing the US as well, so surprise was negated. They could not match US troops face to face, and often mass charges were used to break lines, which required superior numbers. The leadership was very central, many of the Veitcong leaders were on the ground with their troops. Finally, we see that through zealous support of an ideology and the will to die for it, they ultimately broke America's will to continue. A great example of an offensive defense.

2. Hastings showed the attackers in fact could win. Through the efforts of leadership, numbers, and the destruction of Saxon leadership, the Normans broke the Saxon army.

3. Agincourt was a prime example of the consequences of poor leadership. It also shows the effectiveness of a well organized and prepared defense.

4. See Vietnam.

5. See Vietnam, though I would like to add that this is an example of defense to delay until the supporting offense, which encircled the 6th Army.

6. See Vietnam.