How about Chile, for example? They had a left-wing front consisting of socialists and communists that came to power without any violence through a purely democratic process, was fairly popular with electorate, and then got forcefully overthrown by CIA-backed military junta in 1973 (cause surprise-surprise: a socialist/communist state in South America was not in US's interests, and it was a cold war era).

There is nothing inherent about transitional government or even violent overthrow of a current system, communism in its purest form is only about creating the economy that distributes wealth according to people's needs. It doesn't automatically describe the means to get there, and what was conducted in 20th century was an attempt to implement one of the ways mapped by 19th-20th century thinkers.

Some communists will say the general direction was right, but the implementation wrong; some others will say the approach itself was wrong and we need to start building communist society in an entirely different way. Both will be communists.