Unavoidable casualties are simply casualties that cannot be avoided. However, there are other phrases and words that can be used to describe unavoidable casualties. These may include terms such as "compulsory losses," "involuntary casualties," "inescapable fatalities," and "unpreventable deaths." Additionally, synonyms such as "inevitable losses," "unavoidable mishaps," and "unintentional harm" can also be used to describe such occurrences. It is important to note that while these terms may differ slightly in their meaning, the underlying concept of unavoidable casualties remains the same. Nonetheless, using different phrases and synonyms can help to add variety and clarity to your writing.