As a term, it can be used fairly loosely. For example, you might say that two radio channels are 'at war' with each other, meaning that there is fierce competition between them, fighting for audiences.

You can use it as an expression in English. For example, politicians could be "at war with each other", or you could describe someone as being "at war with reality", or even "at war with himself". People also describe "being at war with a neighbour", which normally means they are arguing about a fence or a tree, or too much noise, or parking, but it's not actually a physical fight.