Co-belligerents are defined in the Encyclopaedic Dictionary of International Law as "states engaged in a conflict with a common enemy, whether in alliance with each other or not".
On a judgement issued on July 15, 1999 on The Prosecutor v. Duško Tadić case, the International Criminal Tribunal for the former Yugoslavia (ICTY) appeals chamber noted that nationals of a co-belligerent state would be afforded the status of "protected persons" under the Fourth Geneva Convention if they "are deprived of or do not enjoy diplomatic protection.
[6][7] Co-belligerence (Finnish: kanssasotija, Swedish: medkrigförande) was also the term used by the wartime government of Finland for its military co-operation with Germany (who they called their "brothers-in-arms") during World War II.
Finnish reentry into World War II was described as a direct consequence of Germany's attack on the Soviet Union, Operation Barbarossa.
The Allies, in turn, pointed to the fact that Finland, like (Fascist) Italy and (Militarist) Japan, as well as a number of countries including neutral (Falangist) Spain, belonged to Hitler's Anti-Comintern Pact.