Strength

The Strength attribute enhances a Warrior when using attack skills. This is a primary attribute and may not be used by secondary warriors.

Guild Wars description
When you use attack skills, each point of Strength gives you 1% armor penetration. Many skills, especially those related to surviving and inflicting damage, become more effective with higher Strength.

General description
Strength relates mainly to stances and shouts as well as a few attack skills.

Strength is a requirement for meeting some max defense shields.

Even if a Warrior does not utilize any Strength skills, it's recommended that any spare points be placed into Strength, if only for the purpose of dealing a little more damage when using attack skills.

Associated skills
Strength will enhance these strength skills. Most Strength skills are Melee Attacks or offensive Stances. Strength also contains a number of skills related to Adrenaline gain, attack speed, self-healing, defense, movement speed and bypassing or punishing blocking.