What was the principal reason the Federal government spent so much money during the Bush administration?

To fight the war on terror

Explanation:

President Bush's administration spent a lot of money because of the war against terror. The president had increased spending more than 6 of the presidents before his tenure. The president spent almost twice as much as Bill Clinton.

The spendings were so high due to the need to improve security and also because of the Iraq and Afghanistan wars. Lots of money was spent on the invasion of Iraq. These enormous War costs were part of the reason the country suffered the economic crisis of 2009.