'warmongering' originates from English, specifically the compound of 'war' + 'monger', where 'monger' ultimately comes from Old English 'mangere' meaning 'merchant' or 'seller'.

'warmonger' developed in modern English by combining 'war' and 'monger' (with 'monger' in the sense of one who promotes or deals in something); 'warmongering' arose as the gerund/agentive and adjectival form to denote the act or tendency of promoting war.

Originally 'monger' meant 'seller' or 'trader'; over time the compound 'warmonger' came to mean 'one who promotes war', and 'warmongering' came to mean 'actively promoting war' — a sense that has remained stable as a term for aggressive pro-war advocacy.