Following the rules of war. If they don't follow those "rules of war" they aren't civilized (and could even be executed when the wars over for not following those "rules of war").
A country/nation that is fighting with itself. Example: Two brothers fighting in their home is a "familiy civil war."
the civil warfare
guerrilla warfare was the main style
civil war
There were a few technological advancements that directly impacted warfare during the American Civil War. Two things were the railroad and the Gatling Gun.
Gen. Trenchie of course!
guerrilla warfare
Trench warfare.
population
Two USMA graduates and active generals in the US Civil War had published their views on warfare in the 19th century. Confederate General Pierre Beauregard and Union General Henry Halleck each published their ideas on 19th century warfare prior to the outbreak of the US Civil War.
Railroad transport and communicating by telegraph, I guess. Ah yes, submarine warfare.
Juan Martin Diez
mustard gasthe tanktrench warfare. (although begun in the American Civil War)