Congress makes many decisions that impact battlefield preservation. They set the funding level of the American Battlefield Protection Program, the fund that preservation entities apply to help pay for land acquisition outside of the authorized boundaries of the park service. They also set the amount of money available to the National Park Service to purchase land within the boundaries. Finally, it also takes an act of congress in order to change the authorized boundary of an NPS site.
In the recently passed Omnibus Appropriations Bill, passed just before Christmas, Congress addressed all three areas.
The authorized the expansion of the boundary of Wilson’s Creek National Battlefield in Missouri. Wilson’s Creek was the first major battle of the civil war that was fought west of the Mississippi River. The August 10, 1861 battle was a costly Southern victory, and also included the death of the first Union general of the war, Nathaniel Lyon. The adjustment also brings parts of the Newtonia Battlefield, site of two important battles in 1862 and 1864, into the park boundary.
Also included in the Omnibus package was full funding, $20 million dollars, for the American Battlefield Protection Program. This program provides matching grants for the preservation, reclination, and interpretation of endangered battlefield land.
Finally, $2.5 million dollars was allocated for the National Park Service to acquire battlefield land within park service boundaries.
You can read more about these items here.