While preparing my promotion packet, I came across my old review of A. James Gregor’s outstanding The Faces of Janus: Marxism and Fascism in the Twentieth Century.  Highlights:

Gregor provides an elegant and thoughtful history of what
one might uncharitably term the “Big Lie” of Marxism: That it is
diametrically opposed to the theory and practice of fascist dictatorship.  In this work, he probably does more than
anyone else to show that mutual hostility of fascist and Marxism movements has
always primarily been a case of the orthodox hating the heretic more than the

Gregor begins his account by summarizing his major findings
on Mussolini’s apostasy from orthodox Marxism. 
As Gregor’s earlier work shows, Mussolini’s fascism kept much of the
basic Marxist outlook intact, but fiercely rejected its internationalism.  It would be “better politics” to
unite all social classes within a nation for struggle against rival
nations.  In response, orthodox Marxists
throughout Europe joined together not to critique Mussolini’s arguments, but to
impugn the integrity of any socialist wicked enough to buy into them.  As Gregor explains:

For Italian Marxists, the next
step in the logic of denial was to conceive of Fascism itself, together with
its Marxist “apostates,” as venal and opportunistic.  The final step was to see Fascism, in its
entirety, as the suborned “tool of reaction” – since only monied
“reaction” could offer sufficient benefits to those who sought to
profit from their apostasy. (p.21)

This initial response to fascism grew by leaps and bounds;
the Communist International soon codified it. 
After various refinements, Georgi Dimitroff provided the official
Stalinist interpretation of fascism as “the open terroristic dictatorship
of the most reactionary, most chauvinistic and most imperialist elements of
finance capitalism.” (p.31)  Gregor
then expertly traces the evolution of this notion under post-war Stalinism and
the awkward period of de-Stalinization (when the “fascist” features
of Stalin’s rule became especially difficult to overlook). 

Probably the most novel aspect of this work is the
fascinating history of the Sino-Soviet split, and their ideologists’ mutual
efforts to pin the “fascist” label on the other side.  As Gregor explains:

By the end of the 1960’s, Soviet
theoreticians were prepared to argue that the “Chinese leadership”
had transformed itself into an “anti-Marxist, anti-socialist, chauvinistic
and anti-Soviet… bourgeois-nationalistic” movement of reaction… In
their account, Soviet thinkers had recourse to the same list of descriptive
traits that Western academics had employed for some considerable time to
identify fascist political and social systems. (p.71)

Maoists in China similarly began to describe the Soviet
Union as a fascist state, and argue that the Soviet leadership had in some
sense betrayed socialism in order to take the “capitalist road.”  The danger of fascist subversion of socialism
was omnipresent:

“[B]ourgeois” classes
were to be found in both the Soviet Union and Maoist China, where private
property had long been eliminated and the means of production socialized.  As long as any inequality existed anywhere,
class distinctions existed by entailment. 
Where there were classes, one would find fascism. (p.79)

To the modern mind, it is hard to take this
fascist name-calling seriously.  But what
Gregor helps tease out is not that both sides were wrong, but rather that both
sides were right.