Here's a briefing on some of the most important bits:
The war started a 100 years ago, between the Alliance (Democratic interstellar government) and the Syndicated Worlds (Syndics) (Expansionist Corporate Interstellar Government).
Originally the Alliance didn't commit war crimes such as bombarding population centres, even if they had a legitimate target such as a military base in them. This has since changed, most likely due to the degradation of the Military Hierarchy in the Navy, as well as the loss of the crews trained under said Hierarchy. The Syndics being the way they are, they still build their bases in the middle of population centres, the Alliance just no longer cares.
As a follow on, both sides now follow a simple targeting system for enemy systems with their kinetic bombardments. Is it a military site? Then it's a Priority Target. Could it be used to attack against our troops and ships? Then it's a Priority Target. If it's
not a Priority Target, it gets to avoid being bombarded from orbit, or the other side of the system, as long as it's not being a problem. This means, yes, using 'Rods from God' to clear out the enemies fortified in a residential area is a common practise. Or maybe you have just been forced out of the system so you want to do as much damage as possible, so you launch a bombardment at their cities, using the Kinetic Bombardment Weapons, which travel fast enough to avoid being intercepted.
Only two planets have been bombarded so heavily, they basically require terraforming to become habitable again. One Alliance, which was hit first, and one Syndicate, which was hit as reprisal. The only reason more weren't attacked like this is because
both sides found it too problematic for logistics to repeat it.
The use of Chemical and Nuclear weaponry is very common on the ground. Nuclear munitions can also be used in boarding actions. Not sure what warheads the naval missiles use, so can't say if they are nuclear or something else like antimatter.
However, there is a
massive NO NO that basically
all of Humanity (that we know about) (And the Alliance and Syndics aren't all of it, just the by far largest two chunks, with the Alliance near Sol on one border, and the Syndics on the other. The Syndics border the Alliance and 'empty' space on the other... I
think 'Empty' Space is coreward, not sure though.) after a Bioweapons program got loose on Europa, and killed the entire colony there centuries, if not millennia ago. The threat of the bioweapon was so strong they enacted a
complete quarantine of the colony, you could go down, but you never came up. Said quarantine is still in effect to this very day.
As such, even though both the Syndics and the Alliance hate each other very much, neither side has actually publically worked on, or deployed, a bioweapon.
FTL comes in two forms. The 'Jump Drive' which is the original FTL, that works by going to the edge of the system (inside the Heliopause though) and jumping through 'Jump Points' to a nearby star system/black hole's Jump Points. Range is
severely limited as far as humanity is concerned. You don't jump more than about 12 light years and expect to come out the other end... and there's no manoeuvring in Jump Space, so if you miss the target Jump Point, you have to wait until your ship bumps into another one... if it ever does... (Not as far as they are aware)...
Jump Points affect gravity enough that you can't lay a minefield directly on the Jump Point and expect it to last more than 2 or 3 months at most. Unless you constantly move the mines back onto it and refuel them as they expend fuel. At least, I'm pretty sure it's the Jump Point moving the mines, not the Jump Point itself moving...
Jumps between systems takes on average 5-8 days, and the longer you are in Jump Space, the more creeped out everyone on the ship feels.
The 'Hypergate' is basically a
really bit Stargate... like several hundred kilometres across. You jump from Hypergate to Hypergate, and the further the gates are apart, the faster you travel a set distance. This means a 100LY journey may be slower than a 300LY journey. (I think it's not that significant of a difference, but I can't say for certain).
The degradation of the Military Hierarchy previously mentioned, on both sides, was caused by a simple factor. Sheer attrition causing recruits (volunteers and conscripts) being rushed through training, or field promoted to officer without any non-on-the-job training. This means 'Strategy and Tactics' aren't exactly taught...
As such, 'official' Alliance tactics is to stay more or less in a group together and rush straight at the enemy. The Syndics for ma box and stay in their position in the box no matter what. This hasn't helped slow the attrition down.
The attrition is such that even
battlecruisers and battleships, the two capital ships of both sides, and built to last at most 3 years before they just have every system start to fail. When the Alliance probably has around 200 battleships and battlecruisers relatively evenly split (Just a guess and it's most likely to be on the low side by a fair bit. I believe the First Fleet, once deployed, should have around 150 of both combined, and there's still a enough left behind to not lose much territory before the First Fleet gets back.) that each need to be replaced within 3 years, that kind of tells you just how bad the losses on both sides are. The only non-Pyrrhic Victory is most likely ones where you heavily outnumber the enemy.
Before the war started, ships lasted a century or so, and then they just needed a lengthy shipyard refit and repair before they were good to go for even longer.
Engine Drives aren't reactionless, though very powerful and obey the laws of momentum. Despite this the fact they have an inertial compensator allows some lee-way. Meaning ships can accelerate up to .2c within an hour or two (Maybe 3, it's been a while since I read the series so I'm not remembering the exact details). However, sensors can only deal with targets travelling at an apparent velocity of .2c, which means if you are travelling at .1c and the enemy is travelling directly towards you at .1c, you and they can both hit each other fine. But if they are travelling at .11c, you both are going to miss a lot more, and ever bit higher just makes it much, much worse.
EDIT: Forgot to mention: To go with the war crimes of bombarding civilians, you also have the lovely war crimes of killing prisoners of war... or at least, killing them if you can't be certain you'll have a chance of capturing them and taking them to one of the POW camps. There are also no POW trades... yes, this means it's possible for someone who was captured in the 3rd decade of the war to have had grandchildren in one of the camps... Though no children are mentioned in any of the POW camps in the series. Could just be because Syndics treated their POWs worse than what the Alliance most likely did on average, so no one wanted to have children.
To go with this, there's a tradition on both sides of fighting to the death. Including counter-boarding to overload the warship of the winning side which tried to board your wrecked ship. Not sure how common this is though... Just not abnormal to certain degrees.
Okay... maybe I've gone a bit overboard... Can anyone tell I really like the series?