How have government organizations in the past crafted fake content and “truths” that have become firmly enshrined into generations of soldiers and people — in the name of (inter)national defense?

• Mass Psychological Operations (PSYOP): This Wikipedia entry provides shocking reading for people who may not otherwise suspect that anything officially deemed to be factual, is actually a “conspiracy” by power elites
• Abuse of the illusory truth effect: Read this entry to see how effective the technique of repeating untruths/half-truths in a big way over a long period of time is. Napoleon had reportedly observed: “there is only one figure in rhetoric of serious importance, namely, repetition”: whereby a repeated affirmation fixes itself in the mind in such a way that it is accepted in the end as a demonstrated truth.
• Abuse of authority: Which institutions in a country control official statistics, facts and interpretations of the data? Can the people ever be sure that there are sufficient separations of powers to eliminate conflicts of interest? Can any international or influential authority have the monopoly on truth — to dictate or manipulate as needed for “the greater good”?
• Setting up official fact-checker entities: It is great to have officially endorsed agencies that aim to fact-check controversies, disputes and doubts in the mass media — until people find out that such agencies can be manipulated under the table, or, when mistakes in fact-checking occur, they are written off as a matter of interpretation or are simply downplayed with voluminous instances of accurate fact-checks.
• Abuse of censorship and narrative control: These powers, when used judiciously and lawfully, keep the peace. However, when used to silence unwanted dissent… it is the most powerful weapon against truth. Maybe this case could show the relevance.
• Manufacturing facts to mitigate or nullify uncovered lies: It is too easy for powerful entities caught lying to find official scapegoats or deny everything. Much more difficult but much more potent is to stand by the lies, feigning betrayal, reiterating non-verifiable excuses and alibis, and by pre-meditated manufacturing of mitigating “facts” (facts occurring after a lie) — often possible with technology nowadays.
• Selective choice of authority: In controversies where so-called experts are at a loss to provide answers, and they are divided in their opinions, powerful truth-manipulators can cherry pick experts whose opinions are liquid or can be molded by incentives. All other expert opinions are deemed irrelevant, non-existent, or unaccepted by the powers-that-be in that scenario. Usually, huge sums of payoffs are involved, and these can keep the truth hidden for decades until victims manage to gather enough courage, unity, legal and social momentum to obtain justice.
• Gaslighting, equivocal messaging and other PR tools: When an authoritative entity wishes to insist that something that is happening is not the truth, it can simply issue meaningless edicts on opposing opinions, claiming that “there is not enough evidence proving that” (even though there is not enough evidence proving their own case either). Any entity that argues scientifically or statistically against this appeal from authority is outranked, made to feel small, and/or overshadowed by powerful public relations propaganda and double-speak. This is highly effective since most people are too busy with the grind of life to see (and have become desensitized to) the glaring abuse of power and officious actions.