Don’t believe the claims by those on the left — and some on the right — that America is overstretched abroad, says Georgetown University professor Robert J. Lieber.

“[W]e managed to maintain the world’s most advanced and capable military (including a volunteer army), fight two wars plus a global war on terror, and yet at the peak last year we spent just 5 percent of gross domestic product on defense — a figure lower than the average during any of the Cold War years,” Lieber told The Daily Caller.

“The percentage is already on the way down, toward less than 4 percent by the middle of this decade. In short, our world role is affordable provided we make the needed decisions here at home.”

Lieber, who teaches government and international affairs at Georgetown, is the author of the new book, “Power and Willpower in the American Future: Why the United States is not destined to decline.” He says he wrote it to “argue against a wave of fashionable pessimism about America at home and abroad.”

“Of course we have problems — America has always had problems — but the focus on our difficulties is short sighted, exaggerated and ahistorical,” he explained. “I do not claim that America cannot decline, but that our future is a matter of the choices we make, of policy, leadership and will.”

Lieber says that America has significant advantages that place it in a great position to make the 21st century another American century.

“Despite problems, the breadth and depth of our economy and financial markets remain unmatched,” he said.

“Our advantages include our high technology, scientific base, research and development, great universities, competitiveness and entrepreneurship. Our military forces and power projection remain unmatched. Our natural resource base, including an extraordinary renaissance in domestic natural gas and oil production, provides a tremendous asset for our economy, employment and competitiveness. Our population of 313 million is the world’s third largest, and we still have a relatively favorable birthrate. Many of the world’s best and brightest seek to come here to make their lives and careers. Our institutions of liberty and the rule of law are fundamental elements in that attraction. And America’s extraordinary flexibility and adaptability are unparalleled by any large country.”

But in order to remain atop the world stage, America has to have the willpower to overcome some of the challenges it faces, Lieber argues.

“We must find a way to cope with the enormous annual budget deficits, growing debt and mounting costs of entitlements and health care,” Lieber explained.

“We need tax reform and immigration reform. And we must make optimal use of our extraordinary energy resources by focusing not on what is fashionable, but on what is effective.”

Read below TheDC’s full interview with Lieber about his new book, what he thinks of China’s rise and why some like to claim that America is declining:

I wrote this book to argue against a wave of fashionable pessimism about America at home and abroad. Of course we have problems – America has always had problems – but the focus on our difficulties is short sighted, exaggerated and ahistorical. Declinists downplay our enormous underlying strengths as well as the way in which America has managed to overcome successive crisis ever since the late 18th century. The heart of my argument can be found in the book’s subtitle, “Why the U.S. Is Not Destined to Decline.” I do not claim that America cannot decline, but that our future is a matter of the choices we make, of policy, leadership and will.

For those who are uncomfortable with U.S. power and leadership, or with the characteristic rough and tumble of American politics, decline is something to be welcomed. Others simply exaggerate China’s remarkable — but unsustainable — growth trajectory far into the future and downplay the reasons this rate cannot be sustained. For still others, China’s rise is a rebuke to the U.S. for following policies with which they disagree.

Yes! Since the 1950s there have been repeated waves of declinist pessimism. For example, following the Soviets’ launch of Sputnik in 1957, then in 1973-74 after the Yom Kippur War and the first oil shock, again in the mid-1970s after the withdrawal from Vietnam, at the end of that decade with the Soviets making major inroads in the Third World and the U.S. suffering from severe recession and inflation, and yet again around 1987 when it appeared that Japan would overtake us. That was when Paul Kennedy published his bestseller on “The Rise and Fall of the Great Powers,” with the not so subtle message that America was likely to recapitulate the cycle of rise and decline that Great Britain had experienced.

Explain the concept of “Will versus Wallet” in determining America’s destiny.

Those terms originated a quarter century ago with Joseph Nye at Harvard. “Wallet” refers to the material strengths of the United States. But the declinist narrative overstates our material weaknesses. Despite current problems of debt and deficit, of rising health care and entitlement costs, and in restoring strong growth and employment rates, the U.S. still retains unique strengths across all the dimensions by which power is measured. The real key concerns “will” or “willpower” —  i.e., we have the ability to make the right decisions to avoid decline at home and abroad.

Despite problems, the breadth and depth of our economy and financial markets remain unmatched. Our advantages include our high technology, scientific base, research and development, great universities, competitiveness and entrepreneurship. Our military forces and power projection remain unmatched. Our natural resource base, including an extraordinary renaissance in domestic natural gas and oil production, provides a tremendous asset for our economy, employment and competitiveness. Our population of 313 million is the world’s third largest, and we still have a relatively favorable birthrate. Many of the world’s best and brightest seek to come here to make their lives and careers. Our institutions of liberty and the rule of law are fundamental elements in that attraction. And America’s extraordinary flexibility and adaptability are unparalleled by any large country.

We must find a way to cope with the enormous annual budget deficits, growing debt and mounting costs of entitlements and health care. We need tax reform and immigration reform. And we must make optimal use of our extraordinary energy resources by focusing not on what is fashionable, but on what is effective.

Not at all. Declinists have the British Empire in mind, but 100 years ago Britain had already been overtaken in population, steel production, military spending and GDP by the U.S. and Germany. Yet, unlike Britain, the U.S. still maintains an enormous lead over other possible competitors. At market engage rates (the comparative indicator preferred by the International Monetary Fund), the U.S. GDP this year is exactly twice the size of China’s. As for “overstretch,” we managed to maintain the world’s most advanced and capable military (including a volunteer army), fight two wars plus a global war on terror, and yet at the peak last year we spent just 5 percent of GDP on defense — a figure lower than the average during any of the Cold War years.  The percentage is already on the way down, toward less than 4 percent by the middle of this decade. In short, our world role is affordable provided we make the needed decisions here at home.

Develop long-term solutions to make sustainable our entitlement programs (Social Security, Medicare, Medicaid, veteran’s benefits). Reform tax and immigration policies. Bring federal spending more closely into alignment with revenues. This means reducing annual deficits to no more than 3 percent, the average from 1960 to 2007. Make effective use of our domestic energy resources, including natural gas, oil, nuclear power, hydroelectricity and – where practical and cost efficient – solar and wind power, along with sensible energy efficiency measures.

In addition, tort reform would help significantly in managing health costs. It is scandalous that the Obamacare legislation neglected this. Also welcome would be reductions in excessive bureaucracy and regulation.

China’s export-led growth model is unsustainable. It has a dangerous real estate bubble. It suffers from disastrous pollution of its air, water and food chain.  Massive corruption and abuse of power are deeply resented. By some estimates, China had well over 100,000 civil disturbances last year. The model of state capitalism is not likely to be agile or effective as China becomes increasingly developed. Most important, rule by a Communist Party dictatorship will sooner or later become unsustainable.

China’s one-child policy means that China will grow old before it grows rich. Over the next two decades, China’s demography becomes increasingly unfavorable as vast numbers of people retire while the proportion of those in the active work force declines.