Monetarists would likely argue that the severe recession of 2007-2009 was primarily caused by

The answer is "Excessive money supply creating a bubble in some areas in the economy".

Monetarism is a school of thought in fiscal financial matters that stresses the part of governments in controlling the measure of cash available for use. Monetarist hypothesis attests that varieties in the cash supply have significant effects on national yield in the short run and on value levels over longer periods.