stab-in-the-back myth

Etymology
.

Proper noun

 * 1)  The Dolchstoßlegende: a widespread historical myth in right-wing circles in Germany after 1918, claiming that Germany did not lose World War I militarily and capitulated needlessly after having been betrayed by civilian leaders (especially Communists).

Noun

 * 1)  Any denialist myth misattributing failure to internal betrayal.