Complex sentence: The Foreign Office, however, labelled his ideas "dangerous and misleading rubbish", and rejected a characterisation of the Soviet Union as a peace-loving state with no expansionist ambitions whereas the United States was an aggressor predisposed towards preemptive war.
Split into simpler sentences: The Foreign Office, however, labelled his ideas "dangerous and misleading rubbish". Officials there reject a characterisation of the Soviet Union as a peace-loving state with no expansionist ambitions whereas the United States was an aggressor predisposed towards preemptive war.