Glorification of violence, meaning depiction of violence in a positive way, ignoring ethical issues involved and ugly side effects on civilian populations. Engaging but superficial action without reflecting on what hurting and killing people means.
Why should you avoid it? Are you writing a novel that presents a point of view, or are you writing a politically correct piece of pap? If you want to present glorification of violence as a bad thing, then do so - but not because it ticks some point on a checklist of "how to avoid offensive stuff that might keep you off the bestseller list."
People have points of view. Some people do, in fact, glorify violence and war. Some people have a more nuanced view of it - they prefer no war, but will defend their country if they have to. Some people reject it outright - sometimes for well thought out reasons, sometimes because they just don't want to be shot at.
People's views of the enemy aren't simple, either. Some view the enemy as evil - simple caricatures, cardboard cuts of "bad" to be shot and destroyed. Some know that the other guy aiming his gun at you would rather not be there, either - he'd rather be at home, working in a factory or on the farm just like the guys on the other side.
Take a stance on war. Choose your characters to represent those views - and choose characters with opposing views that you'd like to "shoot down." There's your real conflict. People for (and against war) and their reasons. The guys shooting at one another across a battlefield are the result of that conflict in reasoning.
Use the battle scenes as part of your arguments (both sides, for and against war.) Show the effects (good, if you can find any) and bad. Show how it affects the soldiers and the civilians - show how it changes the views of characters with different stand points.
The only thing I'd say not to do is to write a novel about war because it is a popular theme.
War is serious shit. If you're going to use it, use for more than "action packed background for my romance/mystery/adventure/whatever" story.
One of my favorite authors has written a good many novels about wars and why they are fought - and the things that happen in war time besides the open battles.
There are bloody scenes full of dead and dying, both individual and wholesale - everything from a description of a single shot through the eye to (literally) thousands of dead mown down in windrows with blood covering an area of acres.
The point is not to glorify the violence. The point is to make it clear that death and killing are not pretty or desirable.
The battles are a failure of the politicians or other authorities. The content of the battles and how they play out are a result of the people on the battlefield.
The stories are (to my taste) well written. The characters are interesting. The settings are exotic but well described. There's adventure and action, and many smaller things along the way.
Connecting it all, though, is a clear eyed look at what a bloody, horrific, terrifying, deadly clusterfuck war really is.
What do you have to say on the subject?