False flag
Etymology
From the old naval ruse of sailing under a foreign or enemy flag — false colors — to deceive a target before revealing one’s true allegiance and attacking. The maritime phrase migrated into the language of espionage and warfare for any deception that hides who is really responsible.
noun phrase · /FAWLS FLAG/
A covert operation designed to appear as though carried out by another party, in order to disguise its true author.
What it names
The exact handle for deception-by-misattribution — an attack staged to be blamed on an enemy, manufacturing a pretext or shifting the guilt.
Example
Skeptics dismissed the incident as a false flag, arguing it was staged precisely to justify the invasion that followed.
Related idea
Overlaps with the casus belli it is often meant to fabricate; the false flag is the deceptive deed, while the casus belli is the justification for war it is engineered to supply.