Pakistan, Aug. 16 -- Armoured vehicles rolled past the former US embassy in Kabul on Saturday as the Taliban celebrated five years of what they call victory over foreign domination. But the parade was the easy part. Five years after seizing Kabul, the Taliban no longer have the luxury of presenting themselves as insurgents who inherited someone else's failures. Afghanistan's borders and security apparatus are theirs. So are the consequences.

The gravest indictment is their failure to prevent Afghan territory from becoming a sanctuary for forces threatening their neighbours, despite repeated assurances to the contrary. The latest UN Security Council-mandated monitoring report says the Taliban authorities have "continued their support" for...