Even the biggest possible cuts in Pentagon spending under the recent deal between Obama and Congressional leaders would be quite small compared to the reductions in military spending that occurred after Korea, Vietnam, and the end of the Cold War. (That deal lifted the federal debt ceiling in exchange for modest spending cuts over the next decade, plus additional, supposedly automatic cuts to both domestic and national security spending if Congress can't reach a consensus in the future on which specific programs to cut.)
In The Washington Post, Fareed Zakaria has an op-ed entitled "Why defense spending should be cut":
Serious conservatives should examine the defense budget, which contains tons of evidence of liberalism run amok that they usually decry. [. . .] Most of the federal government’s spending is transfer payments and tax expenditures, which are — whatever their merits — highly efficient at funneling money to their beneficiaries. The exception is defense, a cradle-to-grave system of housing, subsidies, cost-plus procurement, early retirement and lifetime pension and health-care guarantees. There is so much overlap among the military services, so much duplication and so much waste that no one bothers to defend it anymore. Today, the U.S. defense establishment is the world’s largest socialist economy.
There's plenty of waste and duplication at the Pentagon. "As former defense secretary Robert Gates pointed out, there are more members of military marching bands than make up the entire U.S. foreign service." After Fort Hood, the military had plenty of money to waste aiding a politically correct, whitewash report that deliberately obscured the causes of the Fort Hood shootings, the motivations of the killer, and how military brass ignored obvious warning signs of danger to come.
As Zakaria notes,
we spend more on defense than the planet’s remaining countries put together [. . .] It is not unprecedented for defense spending to fall substantially as we scale back or end military actions. After the Korean War, President Dwight Eisenhower cut defense spending 27 percent. Richard Nixon cut it 29 percent after Vietnam. As tensions declined in the 1980s, Ronald Reagan began scaling back his military spending, a process accelerated under Presidents George H.W. Bush and Bill Clinton. Given the enormous run-up in spending under George W. Bush, even if President Obama made comparable cuts to that of those presidents today, defense spending would remain substantially above the levels under all those presidents. The Bowles-Simpson commission’s plan proposed $750?billion in defense cuts over 10 years. Lawrence Korb, who worked at the Pentagon for Ronald Reagan, believes that a $1 trillion cut over 10 to 12 years is feasible without compromising national security.