The term 'brothers-in-arms' is a phrase used to describe two or more people who are allies and fight together for a common cause. It is often used to refer to soldiers who fight alongside each other in battle, but it can also be used to refer to any group of people who are united in a shared goal. The phrase has its roots in the military, but it has become a popular way to refer to any group of people who are united in a common cause.