Questions about the appropriate size of the U.S. Army boil down to disagreements about whether money or the changing national security landscape deserve the most attention, according to a new congressional report.

“For many observers, questions regarding the appropriate end strength of the Army are related to the changing international security landscape, and the perception that those changes are resulting in heightened threats to the United States and its interests abroad,” according to report by the Congressional Research Service, a nonpartisan arm of Congress. “For others, the cost of increasing the size of the Army is the predominant factor in the debate.”

It is unclear how differences will be resolved, the report says. “Although there is a general consensus that the global security environment is becoming significantly more challenging, the role that the U.S. military generally—and the Army specifically—ought to play in advancing U.S. interests is the subject of considerable debate.”

There are reasons why ground forces may be increasingly important, the report says, including “prosecuting military campaigns in which terrain must be seized,” providing deterrence with their mere presence, providing joint force logistical functions and prosecuting so-called gray zones and hybrid warfare.

Ground troops can do things other services don’t, the report says. “More so than remote or offshore military capabilities, the presence of ground forces can send unique political-military signals that can help deter adversaries and reassure allies. This is because the placement of ground forces abroad—which is, in essence, risking soldiers’ lives—communicates a high degree of U.S. commitment to the pursuit of national strategic objectives.”

Ground forces also are useful when military operations must take place in the middle of a local population, such as peacekeeping and stability operations, and counterinsurgency missions. These operations need a ground presence and have troop-intensive requirements, “such as patrolling, intelligence collection, and targeted strikes in order to create stability that can subsequently be translated into sustainable political outcomes.”