State the direction of effect on aggregate demand or aggregate supply for each of the following changes in the conditions:

I. The price of crude oil drops significantly due to the application of a new extraction technology known as "fracking".

II. A new strategic pact with a group of neighbouring nations is struck which the federal government judges will allow it to spend significantly less on defence for a few years.

III. A severe recession occurs in a country which has been a major importer of the nation's exports.

IV. A new carbon emission reduction tax is introduced by the government which is imposed on the industry and electricity generators.