About 20 years ago, we entered a new era, characterized by quasi-nationalist movements in the Middle East, terrorist attacks on soft targets in the United States, and retaliation by the United States, aimed at killing terrorists, eliminating their bases, safe havens and training camps, and at disrupting their communications and finances.
The Bush doctrine, established after 9/11, is well understood. The United States has the absolute right to project force anywhere in the world to capture or kill anyone we identify as a terrorist, without regard for the sovereignty of any other nation. This right is limited only by our capability to exercise it. There can be no legal or moral limits at all.
Unfortunately, both George W. Bush's and Barack Obama's application of this principle has been flawed by their obsession with regime change. That obsession has led to failed occupations in Afghanistan and Iraq, to the death of an American ambassador in Libya, and to a continuing disaster in Syria.
It's inevitable that, as it evolves, Bush Doctrine 2.0 will explicitly reject regime change and occupation as viable tactics in the Middle East, and abandon the notion that terrorism and terrorist attacks on the United States can be eliminated. A long, long war of attrition lies ahead.