Big D--
Forgive me if I didn't clarify enough, but rather than an empire causing massive death, I've noted that Communism brings death and destruction in its wake everywhere it goes.
FoA--
I'd have to agree, the concepts of Nazism are worse than those of Communism--and given more time, Nazism's destruction probably would have exceeded that of communism. However, whenever communism is put into practice, it brings death.
Communism is more than simply a flawed theory wherein hard work and risk-taking are punished and laziness is rewarded--it's a form of government that inevitably brings destruction, suffering, oppression, and death. Nowhere has communism been implemented without becoming an oppressive regime.