The US CIA trained and supported the mujahadeen (sp?) in Afghanistan during their fight against the Soviets in the 1980s. The mujahadeen themselves were divided into two main ethnic/cultural groups, one more similar to Iran/Persians and the other more similar to Pakistan, with Bin Laden aligned more closely with the latter group.

The CIA also taught the mujahadeen the ideology that theirs was a just cause, in that they were fighting and kicking out the occupiers of a Muslim country. This ideology turns out to be the central rallying point for Bin Laden today. The US troops in Saudi Arabia are essentially occupying the country, home of the two most holy places in Islam (as well as a hell of a lot of oil). The US are occupiers like the Soviets in his eye and are thus the enemy.