Book or probably(?) series, read maybe(?) pre-2000 in paperback
Science fiction: three races, one warlike and individualistic (win by any means), one seemingly peaceful and rather old-fashioned (not innovators, but good spies and technology thieves), one ultra-capitalistic (succeed or be trampled)
Humans used by all three races as soldiers, agents, whatever they need; book(s) largely about three humans, each serving one of the three races
Science fiction: three races, one warlike and individualistic (win by any means), one seemingly peaceful and rather old-fashioned (not innovators, but good spies and technology thieves), one ultra-capitalistic (succeed or be trampled)
Humans used by all three races as soldiers, agents, whatever they need; book(s) largely about three humans, each serving one of the three races