Alrighty, constructive criticism.
I'll ignore grammatical and spelling errors, because they're problems that are easily fixed. Instead, I'll pick out passages I think need work, and try and contribute some tips on writing in general, as well.
John was in love long before World War III started, and his life was only kept together by his love, his parents died at a young age. He took place in one of the bloodies battles of the invasion, and lived to tell his heroic tale, though he kept it mostly to himself, not wanting to be honored when so many others gave their lives.
This paragraph that describes John paints him as a pretty cliché character. I know that it's a summary, but it could still use a bit of work. The determined, selfless and stalwart defender of the land is kind of overused these days. I'm not suggesting that you have to give your character an interesting twist - although it might help - but rather that in order to overcome the cliché, you're going to want to really flesh out his character. Make him as real and lifelike as possible. Why is he fighting? Is he simply a man to do as he's told? Is he fighting for the love of his nation? Has he ever considered that he might be fighting a losing battle, and that
surrender to stop the bloodshed might not be the better option?
Also, try never to dump that much information on a reader during the actual story - let it come out slowly, through the words and actions of the characters, rather than through narrative exposition.
Anyway, onto the battles themselves. Action sequences are actually surprisingly difficult to write, because you're trying to portray what's happening cleanly and effectively, without muddling your writing. Try and set the scene by describing the scenery, so we have a rough idea of what the battlefield looks like.
""Prepare yourself. The convoy will be here in 30 seconds." Lieutenant said on the radio.
I positioned myself behind a sandbag with a few other militia soldiers.
Something like this, for instance, could use some work. Where are we? The ruins of a city? A deserted grassy plain? A secluded base in the mountains? What were the soldiers doing; how do they feel about the coming battle? Are they nervous? Excited?
You need to describe the scene as best you possibly can. Even smells and sounds can contribute to the overall effectiveness of a scene, if used well.
Instead of telling us what's happening, imagine you've been asked to describe everything going on in a movie. Not only do you have to take into account actions, but also quite literally everything else. Also, just a minor thing, but don't use caps or digits when you write. They detract from the effectiveness of your work, and seem gimmicky.
Several soldiers dropped from the ship. I turned my rifle's safety off, and prepared to fire.
I pulled back my trigger with full force. My rifle began shooting out bullet after bullet.
The least fortunate ones fell right between my iron sights. Falling soon after.
You're being really clinical about what's happening here. I'd recommend reading a couple more books to get a feel for the flow of a battle - Tom Clancy's 'Red Storm Rising' would be pretty good for that - but if you really want to launch right in, use more adjectives. Those lines don't really flow very well, and you could make it much better with a slightly different choice of words. For the middle line, you could try something like:
"My finger curled around the trigger, and I let go a quick burst. The kick was strong, but not unexpected. Taking aim at one particular soldier, I fired again. No smile crossed my face, however, as his corpse struck the ground. More and more men fell, impacting with the ground at tremendous speed, but many more remained alive in the air; their chutes deployed, and firing wildly into our ranks."
That wasn't great, I know, but it's an improvement on the lines you've put up. Maybe keep a war book on hand for inspiration when it comes to battle scenes, in order to make the writing a little bit easier. Anyway, I've gone on too long already, but just try to keep in mind that you really need to let your sentences flow, and to keep your descriptions as vivid as possible. Try and talk about the chaos of the battlefield, and keep up a real sensation of fear, death, disgust, hatred, or whatever emotion you think would be most appropriate.
TL;DR
More descriptions, more passion in your writing, and more detail. Maybe go read some Tom Clancy or the like, because he's pretty much got this genre down to an art.
This is just criticism. Here's how you might have delivered the same message with less ass.
