Drawing parallels between EVE fictional nations and old Earth historical situations is tenuous at best. Still, I think it's worth reviewing a period of time in which slave-manned navies were the norm.
These quotes are drawn from an
online PDF of a scholarly paper.
"In the growing Athenian economy, numerous slaves - perhaps 100,000 - were available to fight. The wealth of Athens enabled it to support numbers of sailors in excess of its citizen population for extended periods. Competition among cities transformed the ability to man large numbers of ships into the necessity for doing so;"
"Athens needed 34,000 men to man the navy that fought against the Persians at Artemisium. At this time, Athens could still field only 8,000 hoplites. From early in the fifth century Athens could no longer man its ships with citizens alone."
"The casualties suffered in naval warfare were also far higher than those in hoplite battles. If 50 ships sank in a battle, up to 10,000 men could die. More than twice that number of ships went down in the largest battles. On the other hand, hoplite casualties in the entire century from 470 to 370 may have totaled only 24,000."
"..., when Athens mounted its most ambitious campaigns - or showed the depth of its resiliency - its navy probably included the greatest proportion of non-citizens. Similarly, it was during the zenith of Spartan power in the 390s that Sparta sent out armies of Neodamodeis. Citizen armies may dominate the 20th century world, but this has not always been the case. It ceased to be the case in Greece by the mid-fifth century at the latest."
From this, we can see some similarities with the Imperial Navy:
- The Amarr Empire is vast, and its Navy is the largest of the four great nations. At the same time, it has a hierarchal, feudal social structure. The Empire's wealth and size may support/require more ships than can be manned purely by the available non-slave personnel.
- Space battles in EVE, when looked at in terms of personnel casualties, appear to be as costly as naval battles in ancient Greece. Lost starships result in a decimation of on-board staff. This may mean that the only way to conduct a lengthy campaign while maintaining the personnel pool would be to leverage valued citizen or Holder officers with large numbers of slave staff.
- The high casualties of space battles may also encourage obedience and cooperation in the slave crew. In essence, they are held hostage by their own vessels. If they perform well and the ship survives, they will survive. If their vessel is destroyed in battle, there is a very high probability that they will die with it.
- Incidentally, this is why capsuleers are a major advantage - the command and control personnel are replaced by a single 'immortal,' and only more disposable staff are risked.
- The pattern of the Empire's early expansion favors incorporation of slaves into the navy. Subjugation of other nations results in a larger pool of slaves immediately available, while it may take generations of religious and cultural assimilation before the conquered worlds are host to sizable citizen or Holder contingents.