Transparency is a metaphoric term that means the passing on of information without modification, specifically without distortion or systematic omission.
Transparency and Mutual Information
Transparency can be formally and quantitatively measured by mutual information
Transparency and Peace
I conjecture that transparency promotes mutual understanding and thereby reduces the risk of outbreak of violence. Specifically, someone who has a suffiently adequate model of another human being would not decide to use violence against that other human being.
Promoting understanding of reality, and thus transparency, is a key objective of academia.
Transparency and Militarism
If transparency prevents violence, any attempt to systematically use violence requires limiting and controlling transparency. This understanding of the old adage that "the first victim of war is truth". This perspective also explains why dehumanised and vilified images (i.e. [mental model|mental models] of those depicted as enemies are an intrinsic component of all military organisation.
Frequently, military organisations and their "culture" also involve an aspect of encouraging soldiers to adopt a dehumanised image of themselves. In part, this is deliberate and in part, it appears to be an inevitable consequence of developing a dehumanised image of the supposed enemy.
Military organisations try to exercise tight control over who their soldiers perceive to be an enemy. However, requiring a dehumanised mental model of some humans but not others is overall an inconsistent model, and people are frequently unable to cope with this inconsistency. I believe that some aspects of permanent post-war (or other post-violence) trauma involve a spreading of "enemy model" elements to the general model of humans, thus making victims prone to use violence against anyone and leaving them with difficult to trust anyone.