What this suffix does
-monger comes from Old English "mangere" (dealer, trader). It forms nouns meaning "trader in X" or "person who spreads X."
The literal traders: fishmonger (fish seller), ironmonger (hardware dealer), cheesemonger, costermonger (street fruit/vegetable vendor).
The figurative spreaders: warmonger (one who promotes war), scaremonger (one who spreads fear), hatemonger, rumormonger, gossipmonger.
The pejorative turn
The -monger that survived into modern literary and journalistic English is almost always negative or ironic. Calling someone a "warmonger" or "scaremonger" is a strong political accusation.
In Shakespeare: "cheesemonger" appears as a mild insult in Henry IV Part 1.
In modern political discourse: "warmonger" and "scaremonger" are powerful rhetorical weapons — accusing someone of deliberately spreading fear or promoting conflict for personal gain.
British vs American usage
In British English, "fishmonger" (fish shop) and "ironmonger" (hardware shop) are still used as neutral trade terms and appear on high street signs.
In American English, these were replaced by "fish market" and "hardware store."
The literary/pejorative uses (warmonger, scaremonger, hatemonger) are universal in both varieties and appear constantly in journalism.