FORWARD OPERATING BASE APACHE, Afghanistan -- On a blustery, subfreezing night in a sandbagged guard tower, Army Spc. Anthony Ross, 24, of Carson, Calif., twisted and spun in a brief dance. Sometimes Ross does push-ups on guard duty to stay alert, sometimes he dances.

His fellow boredom-fighter for the evening, Sgt. Ulisses Monteoncruz, 21, of Los Angeles, looked up, then went back to the tedium of scanning the rolling, muddy terrain behind the base through a night-vision device that rendered it in shades of gray.

Guard-tower duty is seldom exciting, and it’s particularly tedious in Afghanistan in winter, as hundreds of American soldiers in towers across the country that same night were painfully aware. And Ross knew that in a week or two, when he’d rotate off tower duty back to his regular job – patrolling the roads to clear them of improvised bombs – there probably wouldn’t be much action then, either.

For a little while.

Scholars debate whether the war in Afghanistan has been America’s longest, but as one last “combat season” is about to begin before most U.S. troops leave, there’s little doubt that this war has been America’s most cyclical.

For more than 11 years, U.S. and NATO troops have followed an odd annual rhythm, a pattern so obvious – whether measured in casualty figures or the number of insurgent attacks – that Pentagon officials, the soldiers on the ground and journalists alike casually refer to the annual “fighting season.” Generally, they describe it as beginning and ending with the warmer months. The winter lull is ascribed to snowbound mountain passes that prevent insurgents from moving between their refuges in Pakistan and the fighting grounds in Afghanistan.

But that common wisdom isn’t exactly true, and may have distorted the real picture of how the war has evolved, counterinsurgency expert David Kilcullen says. He thinks that the Taliban, hit hard by U.S. and NATO forces in recent years, may have begun cautiously hoarding their fighters over the warm months, biding their time until the Americans leave. Having fighters in reserve will strengthen their bargaining position with the U.S.-backed Afghan government so that they can negotiate the best possible terms in a settlement.

“The insurgents have been in a kind of permanent winter mode since 2010, and because of the election next year and everything else, they’re on a different calculus now, where they basically are not thinking, ‘How do I gain the most possible military advantage?’ but instead, ‘How do I preserve the largest possible force while still staying sufficiently engaged so as to maintain pressure on my opposite number in any future negotiation?’ ”

Kilcullen, who’s been senior counterinsurgency adviser to Army Gen. David Petraeus in Afghanistan and Iraq, says the meaning of the combat lull is so misunderstood that he discourages the use of the term “fighting season” with anyone he works with on Afghanistan issues.

“It’s not as simple as in summer they fight and in winter they don’t,” he said. “If you live through more than a year or two there, you realize that there are a couple of lulls. There’s a lull that happens in sort of the April time frame. That’s the poppy harvest lull, where there is genuinely a reduction in the fighting because people go and harvest their poppy.”