A more thorough explanation:

The Bush Doctrine is a policy that was announced by President George W. Bush after the September 11, 2001 attacks on the World Trade Center and the Pentagon. The policy states that nations that harbor terrorists will be treated as terrorists themselves and may be subject to a first-strike strategy. This means that if a country is found to be supporting or harboring terrorists, the United States may attack that country without warning.

For example, in 2003, the United States invaded Iraq, citing the country's alleged support for terrorism and possession of weapons of mass destruction. This was seen as an application of the Bush Doctrine, as the United States believed that Iraq was a threat to national security and needed to be dealt with preemptively.

The Bush Doctrine represents a significant departure from traditional international law, which emphasizes the principle of sovereign equality among nations. Under this principle, all nations are considered equal and have the right to self-defense. However, the Bush Doctrine suggests that some nations may be more equal than others, and that the United States has the right to take unilateral action to protect its interests.