And so it is true for the people of Afghanistan, where spending for the army and police is programmed for $11.6bn (61% of projected GDP) in 2011. If that doesn't fit the definition of "unsustainable", it's not clear what would.
Not surprisingly, the Afghan people are looking for a way out. They want negotiations to end the conflict. But the United States says no. The US and its Nato allies are preparing for a major military offensive, perhaps the biggest of the war so far, in the southern province of Kandahar.
A poll sponsored by the US army showed that 94% of Kandahar residents support negotiating with the Taliban, rather than military confrontation.
The New York Times reports this week that "in some parts of the country, American and Nato convoys are already considered by Afghans to be as dangerous a threat as Taliban checkpoints and roadside bombs, raising questions about whether the damage" to the perception of US forces caused by the continued US killings of Afghan civilians "can be reversed to any real degree".
"'People hate the international forces,' said Bakhtialy, a tribal elder in Kandahar. ' ... Their presence at the moment is too risky for ordinary people. They are killing people, and they don't let people travel on the road.'"
A series of high-profile atrocities by US and Nato forces that have surfaced recently has made matters worse. Three weeks ago Nato admitted that US special operations forces had killed five civilians, including three women, two of them pregnant. Nato had previously engaged in a cover-up, claiming that special operations forces had "found the bodies of three women who had been tied up, gagged and killed".
Meanwhile in the United States, a rebellion is growing in Congress against the war. Wisconsin Democratic Senator Russ Feingold, House Democrat Jim McGovern from Massachusetts, and House Republican Walter Jones from North Carolina have introduced legislation that would require President Obama to establish a timetable for withdrawing US troops from Afghanistan. The bill has quickly picked up 29 co-sponsors, and could reach 100 within the next few weeks.
How does this get us out of Afghanistan? My colleague Robert Naiman of Just Foreign Policy explains:
"A signal like this is likely to have dramatic political effects in Afghanistan, just as these things had dramatic political effects in Iraq. In 2007, Congress never succeeded legislatively in writing a military withdrawal timetable into US law. But the fact that the majority of the House and Senate went on the record in favour of a timetable had dramatic effects in Iraq. It put pressure on the Bush administration to compromise its objectives, to start serious negotiations with people it had previously been trying to kill."
The result was a signed agreement between the US and Iraq for a timetable to withdraw US troops.
That is how the Afghan war will end. The pressure will build until President Obama and his military have no choice but to begin the US exit from Afghanistan.
The majority of Americans are against the war, and every week thousands of Americans continue to put pressure on their representatives in Congress, who can also read the polls in an election year. The war has dragged on long after the public turned against it, and long after Washington abandoned any pretence of a coherent story to justify it – a result of our limited, corrupted form of democracy. But this Congressional rebellion is the beginning of the end of this war.