Death toll due to terrorism increased manyfold after 2001
War on Terror coalition experienced attacks after 2001
Total death toll peaked after 2001
If the War on Terror was intended to make the world safer, this graph suggests that terrorism won. But the National Strategy for Combating Terrorism had no clear numerical objectives. It addressed terrorist threats to the US, and no major terrorist attack happened in the US territories after 2001. In this sense, the War achieved something.
Other countries, however, saw more terrorism after 2001. Why? Partly, as a result of the War on Terror. Al-Qaeda itself appeared in response to the Soviet invasion of Afghanistan. And the Bush administration intended to defeat the organization nurtured by war with another war.
The strategists planned to "defeat terrorists and their organizations." It was possible to destroy the terrorist and the organizations, but new ones appeared, such as ISIS.
The Strategy did include the goal to "diminish the underlying conditions that terrorists seek to exploit." The US promised promotion of "good governance, the rule of law, respect for human rights, and professionalization of local justice systems." And also to "resolve regional disputes, foster economic, social, and political development, market-based economies, good governance, and the rule of law."
"Weak states" backfired with more fundamentalism and new opportunities for "regional disputes," such as a new Caliphate. This response is nothing new. North Korea and Vietnam resisted the US at the expense of getting more brutal rulers on the way. North Korea still has one of the strangest dictatorship in the world, and Vietnam is ruled by the same communist party that won the war against the US in 1975.
How to prevent terrorism without creating it? Maybe we knew better if some fraction of the $3-trillion war expenses went to organizations studying economic and political development. They do find workable solutions at the cost of a single Humvee. But instead, most money went to failed ideas, which ended with more human lives lost and new terrorism threats emerged.