Why did President lincoln put general grant in charge of the union armies?

Grant's capture of Vicksburg gave the Union full control of the river and effectively severed the trans-Mississippi region from the rest of the Confederacy. The success of his brilliant campaign caused Lincoln to place Grant in charge of all Union armies west of the Appalachians. In a short time, his forces captured the rail center of Chattanooga and cleared the way for an invasion of Georgia. Lincoln then gave Grant supreme command of all Union armies.