Just how are merchants of death supposed to make a good living these days?

Are the good times really coming to an end, or will Western-led wars be increasingly privatised?

The wars in Iraq and Afghanistan are winding down, Osama bin Laden is dead, and the federal government is deeply in debt. This spells the end of what was a golden decade for the defense industry.

In the decade since the Sept. 11 attacks, the annual defense budget has more than doubled to $700 billion and annual defense industry profits have nearly quadrupled, approaching $25 billion last year.

Now defense spending is poised to retreat, and so are industry profits. “We’re about to go into the downhill side of the roller coaster here,” said David Berteau, a defense industry analyst at the Center for Strategic and International Studies.

Congress agreed last month to cut military spending by $350 billion over the next 10 years. The defense budget will automatically be cut by another $500 billion over that period if lawmakers fail to reach a deficit-cutting deal by November.

Defense industry stocks have already begun to suffer; they are lagging the S&P 500 in recent months. During the last defense spending downturn, which lasted from 1985 to 1997, defense stocks underperformed the broader market by 33 percent, according to an analysis by RBC Capital Markets.

The Sept. 11, 2001, attacks forced the world’s biggest and best-funded military to quickly retool itself. It needed to develop technologies, weapons and strategies to find and fight an elusive network of terrorists that seemed more sophisticated and dangerous than ever imagined.

The U.S. spent $1.3 trillion in the 10 years following the attacks chasing al-Qaida and fighting two wars. That was on top of baseline military spending in excess of $4 trillion.

“After 9/11 the floodgates opened,” says Eric Hugel, a defense industry analyst at Stephens Inc.

The defense budget grew from $316 billion in 2001 to $708 billion in 2011. Federal spending on homeland security, which includes everything from airport security to border control, also rose dramatically. Last year dozens of federal agencies, including the Department of Homeland Security, spent $70 billion on such programs, according to the Office of Management and Budget. That’s up from $37 billion in 2003, the first year after DHS was formed.

All that spending was reflected in the soaring performance of the defense industry, led by the top five defense contractors: Lockheed Martin, Boeing, Northrop Grumman, General Dynamics and Raytheon.

In 2001, revenues for U.S.-based defense contractors totaled $217 billion, according to data compiled by the analytics firm Capital IQ. By 2010 revenues had grown to $386 billion. Profits grew more than twice as fast over the same time period, from $6.7 billion to $24.8 billion. Contractors based abroad, such as BAE Systems, also flourished. BAE was the sixth biggest defense contractor in 2010, with $7.2 billion in U.S. military contracts.