For half a century, Saudi Arabia has been a key economic and strategic ally of the United States. As the kingdom’s wealth grew and the scale of its oil reserves became apparent, the links became ever more intense, culminating in the deployment of 500,000 American troops during the Gulf War. Since then, a once warm relationship has become ever more strained, as tensions within Saudi Arabia have grown, the Arab world’s anger with America has become intense and Washington’s suspicions of the country’s Islamic agenda have deepened. Almost a year after the September attacks, perpetrated largely by Saudi citizens, relations...