The Boston terrorist attack on April 15 has once again focused attention on the US' war on terror.

The US launched anti-terrorism wars far away from the US after the Sept 11 terrorist attacks in 2001, and many al-Qaida leaders, including Osama bin Laden, have been killed. However, many innocent civilians have also been killed and injured, which has provoked widespread public anger around the world. Meanwhile, the threat from homegrown terrorists has grown, which has prompted concerns about the domestic security environment in the US.

Despite this, the US' anti-terrorism stance hasn't fundamentally changed, as terrorists have limited capability to cause trouble in the US. The main opponent of the US is still Middle East terrorist organizations, and the terrorists' background is comparatively simple.