Discipline plays an important role in modern warfare whether it is by force and threats or by mutual respect:

Man in battle … is a being in whom the instinct of self-preservation dominates, at certain moments, all other sentiments.

Discipline has for its aim the domination of that instinct by a greater terror … Discipline in battle becomes the more necessary as the ranks become more open, and the material cohesion of the ranks not giving confidence, it must spring from a knowledge of comrades, and a trust in officers, who must always be present and seen.

- Ardant du Picq, 1921.