Easy example: governments, by definition, will spend more money year after year. Governments rarely 'scale back' their expenditures. When 1) taxes cannot be raised and 2) money cannot be raised through treasury bonds, then there is a crash.
Government is bound to follow the boom/bust cycle and brings the rest of the economy with it. Sectors of the economy that heavily rely on government spending like: health care, defence, banking, education, transportation, will crash and it will be sudden.