This is the 479th most frequent Greek word.
πολέμου
"Of war" or "of the war."
The word 'πολέμου' is in the genitive case here, representing possession or association to 'the duration'.
Η διάρκεια του πολέμου ήταν σκληρή για όλους.
The duration of the war was tough for everyone.
In this sentence, 'πολέμου' in the genitive case indicates relation to 'generals', specifying 'generals of the war'.
Οι στρατηγοί του πολέμου συζητούσαν στρατηγικές.
The generals of the war were discussing strategies.
Here, 'πολέμου', again in the genitive case, is part of the phrase indicating 'during the war', specifying the time period.