In the conflicts of the future, the United States will require high-tech, agile, fast-moving, “lean and mean” forces, according to the new strategy that Obama introduced at a rare appearance in the Pentagon briefing room. “The tide of war is receding,” he said. “We have the opportunity — and the responsibility — to look ahead to the force that we are going to need in the future.”

According to the new strategy document and remarks from the president, Defense Secretary Leon Panetta and Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, those forces will have to be smaller and cheaper. After all, Obama said, “We have to renew our economic strength here at home.”

Grunts are expensive. Pay and other personnel costs, which run about $154 billion this year, make up about one-quarter of the defense budget. And they’ll be fast-acting budget cuts: Unlike trimming the multiyear contracts to build jet fighters and submarines, personnel cuts take effect immediately. Get rid of one soldier and his pay instantly stops. For that reason, presidents and Congress have almost always turned first to manpower when contemplating deep defense budget cuts.