Speculation

Troops is a common term used for units that aren't commanders.

A ruler can promote a troop to the position of Warlord.^Erf-b1-p079 This seems to be uncommon. Some possible reasons for this rarity:

Prejudice^Erf-b1-p079
Expense, similar to the promotion to Heir Designate^Erf-b1-p079 - popped warlords cost time, not Shmuckers
High minimum level requirement few troops reach - though this seems unlikely considering Wanda being able but unwilling to promote from Stanley's remaining 200 living troops.
Troop type restrictions (Men only?)
Maximum current warlord limit (a side may only promote when they have <X warlords or <Y commanders?) - Stanley only promoted one at a time. It is unknown how many warlords King Saline IV had when he promoted Stanley.
Promoted warlords are generally infrerior to popped ones

Troops