What gains did union forces make in the western part of the confederacy in the first two years of the civil war?

Gained control of the Tennessee and Cumberland rivers, two important waterways that extended down to Alabama.

Won the Battle of Shiloh, where the highly-respected Confederate commander General Sidney Johnston was killed. This denied the Confederates the use of the main rail crossroads in the West.

Launched the campaign against Vicksburg, the last Confederate stronghold on the Mississippi. By the end of Year 2, Grant was well on the way to capturing this river-port, despite mighty obstacles, geographical and political.