When I had delusions of being a eurogame designer, the worst part of the whole thing, besides finding out that Uwe Rosenberg had already come up with an idea two years before I did, was pitching games to publishers. I invested a lot of time and energy carefully drafting emails that would, I hope, convey the essence of the game without getting into too much detail but also without making the game sound too simple and also without saying anything that would turn them off. It was an exhausting process, and what made it more exhausting was the fact that most of the time, the publisher would ask me to come to a convention and pitch the game in person.
If I was bad at writing those emails, I was worse at trying to do a five-minute presentation-slash-teach of one of my games in a noisy exhibition hall. No matter how often I had practiced and honed my little speech, I would forget half the words in the moment, and a white hot panic would take over, which probably made me sound like some kind of crazed maniac and not someone that a reasonable person would want to work with. Very quickly, it was confirmed that I didn't have the "knack" for pitching games to publishers in person, and I wasn’t much better at it via email.
This didn't really surprise me, because during all my previous creative endeavors, it was readily apparent that though I had the ability to create in a given medium, I didn't have the ancillary skills to turn it into any kind of professional career. And it seemed like with the eurogames I was in the same boat, where I could do the thing itself, designing the game, but I lacked the skills I needed to find it a home. Now, there's more to it than that - there are reasons why those particular games couldn't sell beyond my own inability to sell them - but at the time I wasn't fully cognizant of that, and felt subtly aggrieved that things that had nothing to do with the design itself were preventing it from being published.
This wasn't nearly as much of a problem with wargames, however. No wargame publisher ever asked me to travel hundreds of miles to a convention to pitch them the game in person. They were content to go off of the information in my email and, if they were interested, in the rules themselves. I felt significantly less pressure on me to finagle the email so that it was just-so; I could just tell them what the game was about, and more importantly, how it was about it (more on that in a hop and a skip), and they understood what I was saying. We spoke the same language.
This was helped I think by one of the fundamental differences between eurogames and wargames. Games are a little like machines in that every part must contribute something to the whole and work in concert. This is equally true both of wargames and eurogames. But broadly speaking a wargame machine - a paper time machine, to borrow Dunnigan's phrase - has the purpose of engaging with and exploring a particular conflict or era. So a wargame designer can concentrate on explaining what the machine does - the history it engages with, and how the mechanisms contribute to that engagement. A eurogame designer doesn't always have this privilege, as the theme is often regulated to mere window-dressing. A eurogame machine's purpose is itself. There's an onus for that machine to distinguish itself by the novelty and elegance of its gears and sprockets - its mechanisms, figuratively and literally. A wargame machine has no such onus. The meaning in wargames are created in aggregate, by a number of different moving parts acting together and sometimes in opposition. This is much harder to distill into a sort of an elevator pitch, and wargame publishers in my experience seem to understand this and allow for it.
So I want to stress that in my experience, pitching to a wargames publisher is much more relaxed than pitching to a eurogames publisher, and you don't necessarily need to be an expert salesperson to get a publisher interested in your wargame. That being said, you want to be respectful of the publisher's time, and you want to assume good faith.
You can be passionate, and passion can sometimes lead to verbosity. That's not necessarily a bad thing. While it's true that Shakespeare wrote that "brevity is the soul of wit", he also did so in his longest play. Wargames are complex and if you want to geek out about your game at length, that's fine, but only up to a point. Once we asked a designer for more information on his game, and rather than answer, he asked us to read a forum thread that had been active for over a decade. That's the sort of thing you want to not do. (In what probably says too much about me, I did in fact stay up late reading over ten years of forum posts about the game, which didn't actually answer any of my questions.)
There are designers who seem reticent to tell publishers anything about their games because they're convinced that if they do, the publisher will steal the idea. No one is going to sign a contract agreeing to publish the game if they don't actually know anything about it. We've run into this more than once, and we're not sure why it's so prevalent. The whole attitude (and the unspoken assumption of bad faith) will sour things right quick, where even if the game was the bee's knees, we wouldn't want to touch it. It's usually coupled with someone who insists their trademarked game system is going to cause a seismic shift in the industry akin to the introduction of CDGs. In at least one case, that game system revolved around the innovative concept of rolling a die and hoping the result was higher than a target number.
"Pitching" doesn't have anywhere near the same mystical significance with wargame publishers, and they don't have anywhere near the same expectation that the designer also be a salesman. And that is one reason why I was able to sell wargames but unable to sell eurogames, and why, eventually, Mary and I started a company with the intention of publishing wargames.
Once we put on the publisher hat, we then were in the position to receive submissions from designers, many of whom are trying to find a home for their first game. Publishing board games is the best job in the world, but the absolute worst part of that job, the hardest part, is telling first-time designers "no". Especially because, not too long ago, I was myself in that same position. I remember how very important my first "yes" was. We love being able to be someone's first "yes". We hate being yet another "no".
We want a reason to say yes, and what we're looking for is that reason. You don't need a perfect pitch, but you do need to give us a reason. The late Roger Ebert often said that a film isn't about what it's about, but how it is about it, and the same is true of a board game. Don't just tell us that it's a game about D-Day. Tell us how the game is about D-Day. Tell us what the focus of the game is, or through what lens it views the event, or what kind of decision space the players must contend with. Tell us why this is your D-Day game, and nobody else's.
All you need to do is get that across. In my experience, that's actually fairly easy to talk about. If you're unwilling or unable to describe the focus of the game, you might need to ask yourself if it in fact has a focus. If you can't describe the decision space, you might need to ask yourself if that decision space exists, or if it is compelling. If you can't describe the game, there exists the possibility that the game isn't there to describe, at least not yet.
Related article: A Good Fit by Tom Russell discusses fitting your game to the right publisher.