The United States will confront numerous unpredictable security threats in the next several years, top military officials told the House Armed Services Committee Friday.

Navy Adm. Eric T. Olson of the U.S. Special Operations Command and Marine Corps Gen. James N. Mattis of the U.S. Central Command were discussing budgetary concerns before the committee.

Olson said the United States and its allies face a range of security challenges that make the future of warfare “complex, unpredictable and unstructured.”

Those challenges include the decentralization of al-Qaeda’s network and lone wolf terrorist activity. Revolutionary upheavals in the Middle East and destabilizing forces in Latin America, Africa and Asia will also present major challenges.