Many wargames utilize a fixed number of turns, which makes sense: if each turn represents an hour, and the battle lasted ten hours, voila!, the game consists of ten turns. Particularly in conflicts with clearly defined attacker-defender roles, this puts pressure on the attacker to accomplish something of value before the tenth turn, and it gives the defender something to focus on: three more turns left, I just need to hold out for three more turns, now two more turns, almost there.
I've used it myself in only a third of my wargame designs. Partially this is because in most of my games, the time scale is fungible. Each turn doesn't last an hour, or if it does, because the activation mechanism has us concentrating over here for a few turns and then over there for a few turns, the hour represented by the fourth turn might be "actually" happening simultaneously with the first. But a more important reason is that many of my two-player games are obsessed with my holy design trinity of tempo, momentum, and leverage. Players put pressure on one another, poking and prodding and threatening to steamroll over the other guy. I don't need the game telling me I have to get something done in the next three turns, because the guy on the other side of the table who's 2 VP from clinching it is implicitly daring me to do something, anything, and now, to stop him. That, for me, is a lot more exciting than watching the Game Turn marker inch closer to the last space on the Game Turn Record Track.
"The Defence of the Eagle's Nest", Alexey Popov, oil on canvas, 1893.
Of course, if the game doesn't have its own timer to gently nudge the two armies into collision, the onus is on the players then to play well and to make their game an exciting match, which is going to have certain pitfalls. I once had someone tell me that one of my games was hopelessly broken as, since there was no limit to the number of game turns and since the movement rules allowed players to move "any, all, or none" of their units, both players could just sit there and never move a single counter, and so the game would go on forever. I asked him if he had played it that way, and he said no, but someone could. I've yet to encounter anyone who goes to that extreme, and I can't imagine someone doing it except out of a peculiar, rules-lawyerish spite, sitting there for hours, sitting there still, sitting there until the end of time feeling quietly superior to the game designer who failed to put a cap on the number of turns.
But, setting that fellow aside, games with a potentially unlimited number of turns can still stall out and drag on needlessly, especially if the players haven't yet obtained the experience and skill level necessary to play the game well, to seize that tempo, ride that momentum, and distort the game in their favor. This is especially true of a game that has a steeper learning curve. Recently, I wrote about difficult games with steep learning curves, and how they can sometimes lead to a bad first impression, but as a designer I'd rather risk that if it results in a deeper and more interesting game. If someone thinks the game is badly balanced until they learn to play it well, I'm not going to lose sleep over that. But, and this is perhaps somewhat ironic, what I will lose sleep over is the idea of a one hour game that plays in three. My designs, for all their peculiarities, follow Dr. Johnson's admonishment: Nothing odd will do long. This also folds in rather neatly with my desire not to punish a losing player for longer than is necessary.
So, in a game without a strict cap on the number of turns, in which players dictate the flow and tempo of the game, how do you keep it short? Well, one thing you can do is turn it into a race: turn a common element of the game into a timer, and when that timer runs out, the game is over. Causing the game to end might not necessarily be the same as winning the game, though in practice you're going to want to end the game when you're going to win it, or you're going to want to maneuver your opponent into a position so that they're forced to end the game and cede to you the win. That for me is an important element: the time element, while somewhat obvious, should still be slippery to get hold of, a dangerous and double-edged sword. This is a pretty common feature of euro-style games, to the point where "when this thing runs out, the game's over, so it's basically the timer of the game" is a phrase that’s used a lot in teaching games to new players.
But it's also shown up in a handful of wargames. Jeff Horger used it to great effect in his Manoeuvre. It's a card-driven game in which each player has their own deck of cards. So you're already using these cards to attack, to recover, and to confer some kind of advantage for your side. As you do, your deck gets thinner of course, and when the first player empties his deck, he gets to reshuffle. When the second player's deck is exhausted, however, the game ends. And so both players have an incentive to run through their decks as quickly as they can, so as to get the advantage that comes with the reshuffle, but only one player is going to win that particular race. The other guy now looks at the tiny remnants of his deck, knowing that each card he uses will now bring the game nearer the finish and reduce the options he has available to him, while the first guy has a big fat deck full of possibilities. Winning the deck race doesn't necessarily mean that you'll win the game, though if you're smart you'll try to arrange it in that fashion.
Though it works quite a bit differently, the Combat Commander series is another example where players exhaust their deck to run down the game's timer, and though it's a bit gamey, players can take meaningless "potshots" to run through their decks a little faster if a quicker game is to their advantage. Otherwise, you don't see this a lot in purely kinetic wargames - that is, wargames that are about my guys fighting your guys, bang-bang-bang kerplow.
It's probably more broadly applicable to wargames centered on non-kinetic conflicts, or wargames that focus on the non-kinetic elements. Richard Berg's Dynasty ends when the deck of I Ching Events cards is exhausted, and so the players together have control over how long the game is going to be. Of course, it doesn't need to be a deck of cards running out every single time; in This Guilty Land, game end can be triggered when the supply of 30 Victory Point chits runs dry. Because the game uses the same cumulative scoring system for legislation that featured in Optimates et Populares, passing enough laws so as to get 4 VPs a turn will vastly accelerate the proceedings. The kicker here of course is that if the other player starts scoring 1 VP a turn, now there's a total of 5 VP being removed from the supply each turn - which might help the guy scoring 4 VP a turn more than it helps you!It's probably more appropriate for Optimates et Populares and This Guilty Land because they are, in some respects, "engine-building games", which makes them a better fit for euro-game mechanics. But there are plenty of wargames that take an engine-building approach, particularly grand strategic and multiplayer games, and they might benefit from looking at these sort of player-driven time pressure elements, particularly if they're looking to distill that experience into a shorter and more palatable playing time.