There are several synonyms for the phrase "war effort" that can be used interchangeably depending on the context. One common synonym is "military campaign," which refers to a planned and organized operation by a country's armed forces. Another possible synonym is "battlefront," which specifically refers to the area where the fighting is taking place. The phrase "defense effort" can also be used to describe the actions taken to protect a country from enemy attacks. Additionally, "wartime activities" or "struggle for victory" can be used to describe the collective efforts made to win a war. Overall, these synonyms highlight the various aspects of a war effort and can add depth to any discussion on the topic.