What is the name of the late 60s early 70s war movie that had soldiers from various countries sent to an island to fight?

The movie you're referring to is likely "The Green Berets," released in 1968. While it primarily focuses on American soldiers, it reflects the multi-national nature of military operations during the Vietnam War era. Another possibility could be "The Battle of Algiers," which, although not set on an island, depicts various groups in conflict during the Algerian War against French colonial rule. If you have more specific details, I can help narrow it down further!