In that case, what did these highly trained Oarsmen do when there wasn't a war?
Haul cargo ships around harbors and upstream rivers?
In that case, what did these highly trained Oarsmen do when there wasn't a war?
Sure - but that's clearly an emergency measure. If you go around offering freedom to your slaves if they row for you, that clearly implies that rowing is considered to be a job for free men. Also, if you tried crewing an entire fleet that way, you'd have no slaves left after the war...at Arginusae slaves and metics (resident foreigners) were allowed to row, with the promise of citizenship for all those who participated
Most merchant ships in classical times weren't rowed. Why spend a fortune on food and drink for hundreds of rowers, when the wind is free?
As for what changed, mostly the Black Death. After that, labour was scarce and expensive compared to before 1350, and states could no longer afford to pay huge numbers of oarsmen. They started using convicts and prisoners of war for the job. Venice was one of the last to turn to slave labour - until the early 16th century they still used free men (although they did have conscription in wartime).
There was also a technological change. Instead of the old system of having multiple banks of oars, it became normal in Renaissance galleys to have just a single bank of much larger oars pulled by three, four or five men each. That required much less skill (to stop the different oars hitting each other) and just needed brute force; so it was more suited for slave labour. But whether this change happened because of the introduction of slavery or vice-versa, I'm not sure.
From what I gather, that used to be a question - but more recently it's been decisively settled in favour of triremes having three banks of oars.Many authors who studied the question wonder if a ''trireme'' did not meant ''three ranks of rowers per oar '' as three ranks of oars would have been extremely problematic for naval engineering
I red one theory i found quite insightful:
Steampower provides work (in physical terms that is).
But as long as there is enough human labour to provide that work, why would anyone seek something else?
Steampower in the 18th century came into being because human labour was not as cheap and easily available anymore so that artificial work was viable.
In Greece and Roman in wasn't because they both employed massive armies of slave to do work.
In the middle ages serfs provided the work.
In China there were more people than work needed.
Only when shortage of labour meets a society that has a standard of science high enough to now of steam engines does steampower come into being.