CRUSADE is the one word substitute for :

Religious war

The one-word substitute for CRUSADE is : OPTION 4 Religious war.

Here's why:

• Crusade historically refers to a series of religious wars initiated by Europeans in the medieval period to recapture Jerusalem and the Holy Land from Muslims.

• Horror film is a film that is intended to frighten or scare the audience.
• Primitive construction is a simple or basic structure that is made using primitive methods.
• Game of chess is a board game for two players that is played on a checkered board with 64 squares.
• Religious war is a war that is fought between people of different religions.