Afghan President Hamid Karzai recently banned Rep. Dana Rohrabacher, California Republican, from entering Kabul for alleging that Mr. Karzai and his supporters rule through exclusionary tactics and make money to stay in power.

That the chairman of the House Foreign Affairs oversight and investigations subcommittee was restricted from entering Afghanistan is appalling, given that American taxpayers spend nearly $2 billion a week on the 11‐​year‐​old conflict and almost 2,000 U.S. military personnel have lost their lives for its government. For the endemically corrupt regime and its band of thugs and cronies, this is business as usual.

One real life drama that played out in Kandahar, between Afghan entrepreneur Naseem Pashtoon Sharifi and the Afghan president’s brother, Qayum Karzai, shows how damaging such behavior by those in positions of authority can be.

Like many in the Afghan diaspora, the 37‐​year‐​old Mr. Sharifi returned to his homeland after the fall of the Taliban regime to help rebuild his country and invest in civil society. He pioneered an outdoor billboard company, Arakozia Advertising, and was the editor of the Kandahar‐​based newspaper Surgar Weekly. His media empire became the fourth‐​largest employer in the region, as contracts from banks, wireless phone companies and even NATO‐​led poppy eradication projects came streaming in.

His vibrant business came to an end when Kandahar Mayor Ghulam Hamidi, a longtime friend of Mr. Karzai, arbitrarily raised the municipal taxes on Arakozia’s billboards from 6 percent to 60 percent. When Mr. Sharifi resisted, dozens of his billboards were torched, torn down and destroyed. Threats of violence followed, from anonymous phone calls to intimidation by Kandahar police. Mr. Sharifi was once again forced into exile.

Eventually, Qayum Karzai, a Baltimore restaurateur who also dominates the construction and security business in Kandahar, emerged in Mr. Sharifi’s place. Qayum Karzai founded his own billboard business, Innovative Kandahar Advertising, which charges four times as much, compared with Arakozia. In a devastating 2010 expose, the Toronto Star’s Mitch Potter verified Mr. Sharifi’s accounts. Other Kandahar‐​based sources also confirmed his accusations.

But Qayum Karzai is not the only Karzai involved in such strong‐​arm tactics against his business rivals. Hamid Karzai’s younger half‐​brother, the late Ahmed Wali Karzai, once consolidated his power by acting as both the powerful chairman of Kandahar’s provincial council and by relying on a mafia like network of militias that made millions of dollars by bribing security companies that benefited from contracts escorting NATO convoys.

One diplomatic cable released by WikiLeaks reveals U.S. officials once described the Karzai clan’s grip over Kandahar as a “semi‐​modern aristocracy.” Congressional investigators have found mounting evidence that American taxpayer dollars had inadvertently created a network of warlords that fed the insurgency’s momentum with economic assistance from the coalition. Worse, U.S. military officials say perceptions that power in Kandahar is concentrated in the hands of the Karzai family fuel support for the insurgency.

Rep. John F. Tierney, Massachusetts Democrat, once said: “In this case, the U.S. appears to be inadvertently fueling the very warlordism and corruption that we are pressing President Karzai to curtail.”

So what can be done?

Step one: Establish just criteria and follow a careful vetting process to identify capable, honest and reputable Afghans from within the country and in the diaspora to serve during a one‐​year interim government.

Step two: Of those Afghan government officials where conclusive proof of their criminal wrongdoings will result in conviction, conduct public trials and mete out sentences commensurate with the offense.

Step three: Allow the Afghan people to decide their preferred method of governance, by either traditional means or democratic‐​style elections.

None of this will be easy, but as the saying goes, “no justice, no peace.” If this or similar efforts for redress cannot be pursued, then Washington has even more reason to exit this conflict swiftly. Contrary to received wisdom, Afghanistan’s bloodshed is not solely a result of the absence of functioning central government institutions. Rather, in the process of building those institutions, the coalition put into power a network of warlords contributing to alienation, violence and impoverishment.

Failing to appreciate the depths of Afghan corruption trivializes a primary motive that spurs many Afghans to fight, and many more to give up hope.