Hey Suetonius:
Well, a few minor suggestions:
First...START! (if you haven't already) Sometimes it helps just to be in the thick of the battle. Zachary's right, putting thoughts down in a coherent and enjoyable manner is hard, but if you sit there staring at it .. well, it can be paralyzing. Also, if you were to start an AAR for example, now you have just a little bit of moral pressure to keep going so as not to disappoint your readers. That pressure can help you overcome any hesitation.
I'd start with something small, were I you. I see you're involved with Vicky. Vicky's GC is small compared to the other games, but it can still be daunting. Perhaps focus on one aspect of your game, such as the "Third Hungarian..." war you mentioned. The smaller scope can also help you focus for the next step.
You'll find all sorts of ideas from reading other AARs, and Zachary's idea of focusing on political intrigue is perfectly valid. Some also concentrate on the military aspects, hopping from war to war. I like the idea of focusing on a few key people, especially if you're limiting yourself to one war or one time period. This works even in a 'history book' format, just add a sentence or three describing the character and people will naturally feel an attachment (or dislike, equally useful) for him. For example:
"General Worcester was approaching fifty, a veteran of the Second Hungarian Succession War. He walked with a slight limp from a musket shot and seemed dispirited in the months leading up to the war."
So we know Worcester knows his business - he's a veteran. He's been wounded though, and if he's dispirited...perhaps he doesn't think this third war is a good idea. Will he rally when the fighting starts? Or will whatever's bringing him down overthrow him when the time comes? Readers will want to know. That's far superior to a handful of stats in EU 2, or two descriptors in Vicky.
As for general flow...focus on the important stuff. Since you're not writing game-play style, people don't give a rat's tail if you've mastered Origami Tech and improved your relations with Japan. If we're talking about a war, then they are interested in military techs, in troop compositions and movements, and of course the final peace. You could also talk about the internal political situation up to and through the war, and maybe some commentary on what it's doing to the economy.
It sounds like you know what you want to write though, and not sure how to go about it. Again...my suggestion is..START. Just close this window, and start. It doesn't have to be pretty. Just start writing sentences. "The Third War broke out in 1840. Hungary was upset because the Austrians didn't invite them to a party. The revolt was started by General Worcester. He had 20,000 men in Budapest and seized the city." You'll find the words come easier once you start putting your thoughts down on paper. You can always go back later and smooth the sentences over.
"In 1840 several respected leaders met in Budapest to discuss the fact Austria wouldn't invite them to the good parties. The ensuing arguments were particularly heated as two distinct viewpoints emerged. The first, led notably by Baron Ima Wimp, believed reconciliation was still possible, but in a fiery speech the Lord Mayor of Budapest, Killem All declared that it was time for Hungary to seize its destiny, and anyway the Austrians had that whole German-wannabe complex. Eventually Mayor All won out.
Therefore, they commissioned General Worcester, a seasoned veteran..."
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Also, I think once you start you'll find yourself with plenty of readers willing to offer advice. With some exceptions this is a very friendly forum with people willing to help. They'll tend to tell you what they hope to see and you can take or leave their ideas as you choose.
Another idea I personally use is to find an author you like. You seem to have read some of the AARs .... find one in your style (history book) that you really enjoy. I can offer a suggestion if you can't find one. Then study it. Figure out how that author structures his sentences, what he puts in the AAR and what he doesn't bother mentioning, how much detail he uses. Personally my AAR tends towards the story/fiction end of the spectrum, and I borrow liberally from two of my favorite fiction authors.
Good luck! And remember, it's only the starting that's hard. Once you're actually in your rhythm things becomes much easier.