We say a nation is engaged in when it mobilizes its economy, technology and home front to help its military win.

War Effort

Explanation:

War effort is a technical term that refers to an act done during the subsistence of war or armed conflict by non-combatants or those not directly engaged in the war (usually the civilians or the government) which is aimed at helping the country's armed forces to win the war. For instance, when a nation mobilizes its resources, technology, and citizens to help its military win an ongoing war. The mechanism was adopted by Russia,  England, and the United States during the first and second World War. An example of war effort is the payment of war tax by a citizen to cater for the welfare needs of its military at the war front. Another example is taking up jobs abandoned by military officers engaged in the war or rationing consumers good in the interest of a nation's military.

a.   it resulted in widespread unemployment.