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What is this called? Where someone says "we will defend A against B!" when there is no threat at all to B and it's a completely false and manufactured thought?

Is there a word or phrase for manufacturing a lie about something like this? Making up a false threat or lie about something to take a stand against?

Edit: Apparently a specific descriptor doesn't exist? One needs to be made. A made up statement of false threat to something created to motivate defense against said nonexistent threat, done so for political purposes. Terms with similarity to "false flag" or "crisis actor".