Zeld2.0, nice summary, even if it's not quite correct at times... (hey, I need to find at least *something* wrong!
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One could divide the history of war into a number of rather different time periods, like you did:
1) pre-Greek/roman, with small bands of men hitting each other over the head with blunt objects, killing a few, but not too many.
2) Greek/roman, with large numbers of men with large numbers of pointy sticks, killing large numbers of enemies, and often murdering or enslaving survivors.
3) early medieval, with knights in leather or chain mail armor, butchering men on foot. Not very efficient, but deadly at times. Survivors might be imprisoned if they were nobles (ransom), while commoners might be executed by their enemies, or by bands of thieves. If you happened to be part of a crusade or jihad, you'd be fucked.
4) late medieval, with halbardiers and pikemen kicking the knights' arses, and crossbows/longbows killing them even more. Nobles would be captured, while commoners would again be fucked, but less so than previously.
5) renaissance, with early muskets and pikes. Cavalry could still play a big part, but would often be thwarted by the pikes. Cannons also appeared, *with* exploding shells, which could devastate the infantry squares; and without squares, the cavalry would kill them... Survivors might expect some decency, but not always, depending on the enemy involved.
6) late renaissance, with more advanced muskets and cannons. During these days, battle turned into sieges, with everyone fighting for control of key fortresses (to control the land). If a fortress was finally captured, the people inside might be exterminated if the attackers were pissed. Sometimes they were spared, though.
7) revolutionary wars, with massed conscript armies and such. Napoleon and his French armies are a good example, as is the American war of independence. People fought for a cause, and morale was much higher than before. Lines of troops would advance and be exterminated by lines of enemy riflemen. This period also saw the introduction of snipers to pick off enemy officers (US vs Britain). Survivors might be treated well, but not always. It depended on the commanders, basically.
8) early modern, with bolt-action rifles and high-explosive siege shells (war of 1870 between France/Germany is a prime example). Brick and mud fortresses were reduced to rubble easily, and the wars would be faster than before, with more movement (trains). There are some prime examples of good behavior against defeated foes, but also some nasty reports of executions.
9) WW1, with trenches and concrete fortresses, machine guns, huge amounts of artillery and poison gas. Nasty. Only the introduction of tanks (as well as planes and shock troops) managed to break the deadlock. Prisoners would be send to large prison complexes, where they might be well-treated if lucky. Russians in Germany would often starve to death because Germany couldn't even feed their own population thanks to the British blockade...
10) WW2, with tanks, bombers and fast movement. Depending on the theater of operation, combat could be brutal and deadly, with survivors being pretty much fucked (Russia), or relatively lucky (France, Italy, especially Africa).
11) post-WW2, with more tanks, bombers and even faster movement. Oh, and atom bombs and such... The Geneva convention is upheld by some, not by others, so depending on the situation, you're treated well or shot.
There, that's my version.