When two or more things are involved in pursuit of an outcome, either those things are with or against each other.
In war, the US government goes to war with a government against a government or if not that, then the US government goes to war against a government, where "with," or having an ally, isn't involved.
Is this topic about the US government going to war with or against Syria?
School's fine. Just don't let it get in the way of thinking. -Me
Study nature, not books. -Walton F. Dutton