"Five times in the last 90 years, the United States has disarmed after a conflict: World War I, World War II, Korea, Vietnam and then the Cold War," testified Defense Secretary Robert Gates on Capitol Hill in March.

Will Iraq make six?

The chairman of the House Appropriations defense subcommittee, John Murtha, D-Pa., recently predicted as much. He snapped his fingers for effect and said he expected procurement funding would dry up once the Iraq war ends. Unfortunately, political pressure to reduce defense spending overall is growing. A general perception holds that the battle in Iraq constitutes the entirety of the war effort, so when major combat operations there wind down, the American people would be entitled to a new peace dividend.

Here's the difference: The last five times we demobilized after a war, we'd mobilized first.

The Iraq war was not only fought without prior mobilization, but it followed a decadelong procurement holiday. If our country cuts the defense budget now without considering America's worldwide responsibilities or the likely geopolitical landscape the U.S. will face over the next five to 10 years, we're setting ourselves up for disaster. That's especially true because the U.S. does not spend enough today to meet its security commitments beyond Iraq.

Global stability

America's interests span the world, and the military has global reach and responsibilities. The primary purpose of the U.S. military is to deter and defend the homeland. When required, America's military must fight and win wars to protect our security interests. Success requires a military capable of defeating traditional threats posed by nation-states, transnational threats such as terrorist organizations and organized crime, as well as dangers derived from state collapse, such as piracy. We can't just pick which enemies we want to fight in the future or "threat-away" challenges by ignoring potential future conflicts.

Employing military power involves successful direct action as well as engagement and the presence of U.S. forces abroad. It's everything from a show of force to power projection and also includes training indigenous military elements. U.S. forces also provide protection for America's friends and allies and bolster their military capabilities. We maintain a substantial deterrent force on the Korean peninsula, have overseen Japanese security for the past half-century and uphold security guarantees to Taiwan.

Similarly, in the Middle East, the U.S. military presence contained the expansive ambitions of Saddam Hussein, decapitated the belligerent leadership of Iraq and Afghanistan, conducted nation-building aimed at helping these two countries on the path toward modernity, ensured continued access to affordable petroleum for itself and the global economy, committed to the protection of Saudi Arabia, and balanced against the unpredictable actions of Iran following the overthrow of the Shah in 1979.

Further, America's nuclear weapons and missile defenses act not only as deterrents against and protection from attack, but also serve to alleviate the concerns of our allies so they do not have to develop their own potentially destabilizing strategic arsenals.

In addition, America's military does more than fight. Because U.S. economic growth is connected to the stability and prosperity of the global economy, the nation uses its naval capabilities to protect sea trade, thereby ensuring all maritime assets may transit freely and safely. Eighty percent of international trade and 67 percent of petroleum is transported by sea; fully one-quarter of global trade passes through the Strait of Malacca alone, and one-third of the U.S. gross domestic product (GDP) is derived from trade.

Additionally, when humanitarian disaster strikes, a strong military enables policymakers to commit our country's unique and vast resources to assist the country in need, such as after the 2004 tsunami in the Indian Ocean and following a devastating earthquake in Pakistan in 2005.

Critics of America's defense spending often point to the size of its defense budget compared with global spending in an effort to argue for reducing America's hard-power capabilities. The U.S. defense budget in real dollars is on par with spending by the rest of the world combined. Many question how such a massive budget can be justified, even during wartime. The Cold War may be over, but the U.S. still has global interests and global responsibilities, and they cannot be protected on the cheap.

Those who have argued that America's defense budget is too large also protest that it could be reduced if only our allies would invest their fair share. It is true that the defense budgets of European and even some Asian powers are on the decline, but as Rep. Ike Skelton, D-Mo., chairman of the House Armed Services Committee, has argued, "To depend on allies to carry out our strategy is the height of folly." While it would be a positive development if France, Germany and Japan were to spend more, America cannot reduce its own budget while compromising security in the hope that others will fill the void. If allies were to increase defense budgets, America could consider adjusting its own. Until then, it is irresponsible to cut spending while crossing fingers and hoping for the best.

Military primacy

Strategy always changes faster than force structure. Paring defense budgets to what Washington wishes to spend can be justified by adopting a more modest and restrained strategy. When demands change, as happened with the outbreak of the Korean War, strategy can be modified -- but it may take years to field forces adequate to implement abrupt changes. In the meantime, the cost of being unprepared is often measured in the lives of men and women in the armed forces and the national security of the nation put at risk. Because every potential threat cannot be predicted and because procurement cycles typically take decades to field a particular system, the U.S. military must plan its forces around a grand strategy and hedge with specific capabilities to meet any future requirement. Those core capabilities -- many of which are possessed today -- should be the mainstays of strategic planning. They include protecting and defending the U.S. and its allies against attack; air dominance; maritime control; space control; counterterrorism; counterinsurgency; the ability to seize and control territory against organized ground forces; projecting power to distant regions; and information dominance throughout cyberspace.

To anticipate and cope with a shifting strategic environment, the U.S. must continue to have the most highly skilled and professional military force, equipped with the most capable weapons systems. America's robust military budget allows the development of unchallenged capabilities that provide numerous benefits. These capabilities are not immune to atrophy, age, budget cuts or apathy and require steady investments in next-generation platforms to maintain the advantage of unchallenged military capabilities.

As a percentage of GDP, American defense spending is historically and relatively low. Since Sept. 11, 2001, the U.S. has spent about 3.8 percent of its GDP on defense. That's well below the 5.7 percent we averaged over the last 40 years. This includes the 1990s' "procurement holiday," from which today's military has not yet fully recovered.

Defense budgets are projected to fall dangerously low within five years. The Bush administration's current budget proposal shows the defense budget declining to 3.2 percent of GDP by 2012. That would not be enough to meet military requirements, even if we enjoy robust economic growth.

While the defense budget is indeed substantial in real dollars, it matches the current and future global responsibilities of the U.S. To adequately provide for the common defense and secure America's vital interests, Congress should commit to funding the core defense budget at roughly today's levels of 4 percent of GDP for the next 10 years. The sum of America's global responsibilities, and the costs to fully equip, train and compensate a professional all-volunteer force, require today's investment levels.

Peace rebate redux

Banking on an end to the ideological struggles that defined the 20th century, the Clinton administration -- with the full enablement of a Republican-led Congress -- chose to cash in on a peace dividend. Starting in 1992, drastic cuts to military end strength and recapitalization that skipped an entire generation of weapons were so dramatic and severe their effects are still felt today, even with real dollar increases in the defense budget since 2001.

The active-duty Army was slashed from 18 divisions during Operation Desert Storm to 10 today, although it's now growing again. The Army began the Iraq war with a $50 billion equipment shortfall and must recapitalize or replace nearly its entire fleet of vehicles. The Navy, which consisted of almost 600 ships at the end of the Reagan administration, struggles to sustain a fleet of 280 today. While spending a recent average of $12 billion per year on shipbuilding, the Navy's current modernization plans actually require spending a minimum $17 billion for the next 30 years to reach a 313-ship fleet. The average age of Marine Corps helicopters is 25 years. While the Pentagon bought an average of 238 fighter aircraft each year from 1975 to 1990, it bought only 28 per year from 1991 to 2000. The Air Force must plug the dramatic fighter gap, purchase more next-generation fighters, meet its growing strategic airlift requirement, build a new tanker and develop an interdiction bomber to replace the B-52, an aircraft almost 50 years old.

However, the greatest irony of the post-Cold War budget cuts is that as America's military force was reduced, the tempo at which it operated increased.

America's military could soon pay a heavy price for any replay of the 1990s' peace dividend. Except this time, there is a gap between the perceived and actual pace of peacetime operations. U.S. leaders are employing the military at a breakneck pace. During the Cold War, the Pentagon took part in more than 50 operations. Alternatively, since the Gulf War 17 years ago, the military has engaged in almost 100 operations. Over the past 15 years, the U.S. has asked its service members to do much more with less of everything.

Funding for immediate operations has come at the expense of the long-term health of the services. Each service must purchase new systems after years of procurement underfunding while major combat operations persist. There is little justification that these urgent spending priorities are unnecessary or they can be delayed further. The current military procurement budget is about $81.3 billion. A Congressional Budget Office study in October 2006 predicted the Pentagon may need as much as $80 billion more in 2008 alone to afford current programs, pay personnel and fund ongoing operations. When the services must choose between equally important priorities to pay for short-term operations or force service members to incur increased and unnecessary risks, the nation is not spending enough on defense.

The current, substantial commitment of U.S. forces in Iraq alone will require a massive program to recapitalize and replace equipment. While the operational tempo of the U.S. military during this larger war will vary over time, the conflict will require a generally elevated tempo. The search for a peace dividend is unwarranted because the global war on terrorism goes beyond Iraq. The climbing average age of ships, aircraft, vehicles and many other weapons systems and platforms increases risk for all of the services while reducing their ability to execute their missions. No rational justification exists for reduced defense spending in the near future.

Matching the mismatch

Maintaining a predictable level of core defense spending for the next five to 10 years at roughly today's levels would allow America's war fighters to maintain and build up the capacity to meet the full spectrum of irregular and conventional missions to counter today's enemies and tomorrow's unforeseen challenges. A lack of predictability in defense funding only increases the costs of nearly all major programs. One key to controlling the price of ships, planes, vehicles and other equipment is to minimize fluctuations in the defense budget.

Arguing that the U.S. military should instead focus on irregular threats and refining counterinsurgency skills, shifting from conventional skills and building weapons to counter current threats is a zero-sum exercise. The military must be able to counter myriad threats and possess unmatched capabilities in varying contingencies that are not prioritized one over the other. A deliberate assessment of the likelihood of potential threats and enemies is required before procuring the appropriate capabilities to prevail in future conventional and irregular conflict. Because the lead time on development and procurement -- including training on new systems -- takes years, if not decades, the U.S. military must often hedge when making budgeting decisions.

Funding for the future cannot be gauged on a series of high-stakes bets. The military does not have the luxury of focusing solely on conventional and state versus unconventional and nonstate actors. The U.S. military needs not only the most capable equipment but also a sufficient number of weapons systems and suppliers to meet national security requirements.

Avoiding budget spikes affords more than platforms, however; it provides stability in defense planning and offers a steadier workload for those constructing them. When budget requests change so dramatically year to year -- particularly when requirements stay the same -- the industrial base cannot plan ahead, and this increases the cost of individual systems. The national security of the U.S. is well-served by a competitive industrial base, and defense budget predictability will contribute to this effort.

Spending 4 percent of GDP on defense still would be well below what America has spent during the past 40 years. Although it is true that defense spending in actual dollars has increased substantially in the past decade, as a percentage of our economy, it has continued to decline to historically low levels. Today's defense budget also represents a manageable level of spending that is consistent with government policies that promote economic growth. Unfortunately, when cuts to the federal budget are considered necessary, it is the defense budget that is most often targeted. In reality, the main culprit of federal budget growth over the past two decades has been domestic discretionary spending, which has grown at nearly twice the rate of defense and homeland security spending. Reforming these programs, so as to balance the priorities of the federal budget, should be a primary issue for Congress.

Growing consensus

In the past two years, a consensus has begun to emerge within the defense community to maintain today's levels of defense spending at 4 percent of GDP for the foreseeable future. During budget hearings in February 2007, then-Army Chief of Staff Gen. Peter Schoomaker told members of Congress that the Army will continue to need billions of dollars for at least three years after Iraq operations wind down in order to repair and replace equipment damaged during operations. Former Air Force Chief of Staff Gen. T. Michael Moseley clearly stated there should be a national debate about robust and sustained defense spending. The Chairman of the Joint Chiefs of Staff Adm. Mike Mullen told the Christian Science Monitor in March: "I really do believe this 4 percent floor is ... really important, given the world we're living in, given the threats that we see out there, the risks that are, in fact, global, not just in the Middle East." Gates said he believes that once war funding is passed as part of the baseline defense budget, Congress should dedicate 4 percent of GDP to funding national security.

Congress has begun to engage in a thoughtful debate about the responsibilities of the American military and the resources required to meet these responsibilities, yet more must be done. A joint resolution (H.J. Res. 67 and S.J. Res. 26) introduced last year by Rep. Trent Franks, R-Ariz., and Sen. Elizabeth Dole, R-N.C., seeks to fund America's military at roughly today's levels. Rep. Jim Saxton, R-N.J., introduced an amendment to Section 1070 of the fiscal 2009 Defense Authorization Act (HR 5658) that sought to encapsulate the spirit of this legislation. Unfortunately, it was not included in the House defense authorization bill.

The notion that the U.S. can spend an amount on its national security on par with the world's other advanced states is inconsistent with the realities of America's responsibilities. Absent U.S. leadership, the world is more inclined to a path where conflict and disorder threaten the security and economic vitality of all nations. To sustain security and stature, the U.S. must continue to invest the necessary resources in its military to fully equip, arm and train the all-volunteer force to meet its complete range of mission requirements. Preserving these capabilities will allow America to secure its national interests while continuing to meet its responsibilities to the security of allies and preservation of the global free market.

The military is in a crucial phase of recapitalization. The war-related bills will come due for years after a majority of U.S. forces are withdrawn from Iraq, yet supplemental spending bills surely will disappear. There is no appetite to absorb the supplemental spending into the larger defense budget. In the long term, continuing to underfund defense and then allowing wild fluctuations in defense budgets during times of war will only cost the country more and compromise security at home and on the battlefield, including reducing the defense industrial base to an unacceptably low level. An undercapitalized base is less competitive, which serves to increase costs for the government and U.S. taxpayer.

The challenge is not the resolution of the American people. Rather, it is a matter of communicating national defense requirements and core objectives to policymakers and the general public. A disconnect exists between the civilian population and the day-to-day obstacles facing America's military. Many Americans may not perceive the same current or future threats as defense leaders, making them unable to properly approve the types of capabilities the military must possess.

Members of Congress, the president and presidential candidates should undertake the difficult task of changing public opinion -- not following it -- by reminding the American people that the ongoing war is not over and that the stakes in this war extend to their lives, liberty and future prosperity. For these reasons, Congress and the president must commit to fund the nation's military requirements well into the future. The next president and future Congresses also must commit to providing for the nation's defense through sustained robust defense budgets.

Mackenzie Eaglen is Senior Policy Analyst for National Security at The Heritage Foundation.