I know this question is quite broad in scope and would certainly vary based on which particular time period or war is spoken of. I'm assuming, however, that general statements can nonetheless be made about the treatment of these people.
An example of some such situation: Say I was an upper middle class or even upper class/noble Frenchman, and I traveled to Prussia in the spring of 1870. Then, suddenly, war broke out between the two countries. What would happen to me?
They could be interned, which happened to 110.000-120.000 Japanese people residing in the USA in 1942 after the Japanese attack on Pearl Harbor. Keep in mind that this included both american citizen and foreign travelers and residents. The Japanese people who was interned lived mostly in the West Coast of the USA, and where forcibly relocated to military camps, and had to stay there until 1944-1946(All interned had been released by 1946). The internment of the Japanese in USA was authorized by Franklin D. Roosevelt in his Executive Order 9066, which authorized the Secretary of War and military commanders to prescribe military areas where the Secretary of War or military commanders could expel people at will, and ordered them to proved the expelled people with transport, shelter, food and accommodations (which de facto was interment).
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