Who said that communism and capitalism could not exist in the same world?

The assertion that communism and capitalism could not coexist in the same world is often attributed to various Marxist theorists, with Karl Marx himself expressing ideas about the inherent conflicts between capitalist and communist societies. Additionally, prominent figures during the Cold War, such as Soviet leaders and Western politicians, articulated this sentiment as they viewed the two systems as fundamentally opposed ideologies. This belief was central to the ideological tensions that characterized the global political landscape during that era.