Co-belligerence

War against a common enemy

Co-belligerence is the waging of a war in cooperation against a common enemy with or without a military alliance. Generally, the term is used for cases where no formal treaty of alliance exists. Likewise, allies may not become co-belligerents in a war if a casus foederis invoking the alliance has not arisen. 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".

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