[Petronski]

The notion of fascism and communism as opposites originated as Soviet propaganda during and after WWII.

Not so. In Germany and in France in the 1920s and earlier, the communists sat on the left of the speaker of the legislature, while the fascists/nazis sat on the right. This is the origin of the division between communism and fascism/nazism, and as well is the origin of the terms right and left.

[swilhelm73]

Actually, no.

The left and right, in the modern sense, originates from the French Revolution. Monarchists, businessmen, and the church's followers sat to the right, and the radicals and various other scum and villany who wanted to changes French society wholesale and immediately were on the left. Just as modern communists would be part of the left of the French Revolutionary era, so too would modern fascists.

Fascism, as a phenomenon starts with Mussolini's split from the socialist international over Italian entry into WWI. As a political movement of note to the world it appears in 1922 with his march into Rome.

The Soviets were very interested in fomenting red revolt in Germany, and believed for quite a while that Hitler's rise to be what communism would look like in a modern industrial country. Some communists, most notably Trotsky disagreed, but by this point Trotsky was in exile.

Again, if communism and fascism were complete opposites this confusion becomes really difficult to understand - how could the communist leadership so misestimate what they were seeing?

This, however, becomes rather easy to understand if one considers that communism and fascism are similar philosophies. The communist leadership was, obviously, wrong...but not off by as much as conventional wisdom would postulate.