KABUL, Afghanistan – We know why young American soldiers are here. Terrorism came to America with this return address.

As the terrorists retreated, Afghan-Americans came here as well to start businesses, make money and build an economy.

Six years on, Washington is sending more soldiers to fight the resurgent Taliban and al-Qaeda.

Meanwhile, corruption within the Afghan government is crippling commerce and pushing some Afghan-Americans back to the United States. And they are saying that if we don't want Afghanistan to turn again into a failed state and a sanctuary for terrorists, fighting corruption must also be a priority.

One of those pushed out told his story over dinner last week at a Preston Road restaurant in Dallas.

He'd started a multimillion- dollar business in Afghanistan. Then he joined the government. One day, his boss told him to sign a crooked contract. He refused.

A friend worried that he was putting his life at risk by standing between a thuggish company and a lot of money. His wife said, "I know what you're doing. Look at your children."

So he left, joining what he says is an exodus of Afghan- Americans who found it impossible to do business in a society rated by Berlin-based Transparency International as one of the most corrupt in the world.

"The commercial world is all but over in Afghanistan," he said.

I traded the businessman anonymity for his candor. But others are making the same points, on the record.

Army Lt. Gen. Karl Eikenberry, former commander of coalition forces in Afghanistan, says the greatest threat to success in Afghanistan is not the resurgence of the Taliban but "the potential irretrievable loss of legitimacy of the government of Afghanistan."

Commerce hasn't stopped in the country. Per capita income has doubled since 2002, though that still leaves the average Afghan with an income of about $1 a day. Foreign aid from around the world continues to come. Last year's total was estimated at about $3 billion.

Foreign investors are still arriving. In November, China Metallurgical Group won the bidding to develop Afghanistan's Aynak copper deposits and said it would put $3 billion into the mines.

An Abu Dhabi telecom firm said in August it would invest $300 million to expand mobile phone service in Afghanistan.

Yet the International Monetary Fund has set a priority for helping Afghanistan get control over payroll thefts and bribery.

An Afghanistan study group led by former U.N. Ambassador Thomas Pickering and former NATO Supreme Commander Gen. James Jones released a report last week that suggests the Afghan government should get more recognition for the reconstruction there – but only after tougher anti-corruption measures are implemented.

The same report said stopping Afghanistan's opium economy must begin with "the removal of high officials benefiting from the drug trade in the government."

President Hamid Karzai has admitted there is a problem.

"All politicians in this system have acquired everything – money, lots of money. God knows it is beyond the limit. The banks of the world are full of the money of our statesmen," Mr. Karzai said in November.

He warned his corrupt government colleagues that the Afghan people are losing patience.

"They should know that the Afghan people will rise against us. And this time, there will be no place [abroad] for us to flee."

Mr. Karzai's ambassador to Washington, Said Tayeb Jawad, said that a few high-profile prosecutions of corrupt Afghan officials by the United States or others in the anti-Taliban coalition would have a major impact.

But rooting out corruption within the government, stopping the drug trade and fighting off the Taliban, he said, would be more than his government could handle at the same time.

"Why start another war?" he asked. "You cannot expect miracles."