The correct answer is (A) 1. Any of the military campaigns waged by the Christians during the 11th, 12th, and 13th to recover the Holy Land from Islam. 2. Any war undertaken in the name of religion. 3. Any vigorous movement for the defense of an idea or cause.

Examples of use:

• We have been in the midst of a crusade against AIDS for several years.
  
  
• There was little evidence of Christian charity in the aggression, slaughter, plunder, and mayhem of the Crusades.