What was the reason for sheridans shenandoah valley campaign?

The task of Sheridan's Valley Campaign was:

1 - Carry through the elimination of Early's II Corps of the Army of Northern Virginia, the only Confederate Great Unit which still had freedom of movement to operate

against the left (or Northern) side of Union front and reduce the pressure of

Grant's Army on the Richmond-Petersburg's sector.

2 - To scorch the earth in order to deprive the Confederates of all agricultural and structural resources in being there.

This campaign together Sherman's march to the sea, was part of the Grand Strategy put in motion by grant as General-in-Chief to defeat the Confederacy.