当然是fight against sb,因为两军打仗有对立的意味在里面。而against就是介词“反对”的意思。
举个例子
England and France fought against Russia in the Crimean War.
在克里米亚战争中,英、法两国与俄国作战。
fight with仅仅是说和某人打,没有作战打仗的意思
fight with:
为...而战
fight against:
对抗...
fight against
fight against :to take part in a war or battle aganist an enemy打仗 战斗 这是牛津高阶的解释
fight with:打斗,与...打架eg:Jack is fighting with Ann.
后面那个