What happened to the budget surplus?

Back in 2001, the government predicted a budget surplus of $5.6 trillion between 2002 and 2006. So, what happened to that surplus? This table from the CBO illustrates how recent policies and incorrect forecasting led the government from a $5.6 trillion surplus to a deficit estimated at $2.9 trillion!

Note the two largest factors: $1.8 trillion in tax cuts and $1.6 trillion in increased defense spending.