How is it possible to increase government spending while at the same time report a budget surplus? Besides raising taxes, what other explanations are there? Borrow money (government debt), increase the GDP, lower the interest rate, reduce spending on transfer programs, etc.

Suppose the government's budget goes from a deficit in Year 1 to a budget surplus in Year 2, does it follow that the federal government acted to raise taxes or cut government spending in Year 2? Is there an alternative explanation?