The phrase "was tantamount" indicates that something is equivalent or synonymous with something else. There are several alternative synonyms that can be used in place of "was tantamount," such as "was comparable," "was equal to," or "was the same as." Additionally, "was tantamount" can also be substituted with phrases like "had the same effect as," "was tantamount to," or "was comparable to." It's important to use a variety of synonyms when writing to keep the language fresh and engaging. Experimenting with different ways of expressing similar ideas can also help you find the best way to get your point across.