The phrase "open warfare" refers to a state of conflict or battle where opposing sides are openly fighting against each other, without any restrictions or attempts to hide their aggression.
Sentences with «open warfare»
It was a bitter rivalry which more than once almost resulted in open warfare. (religion-online.org)
As the general election approaches there will be a natural drift towards open warfare between the two parties in government. (politics.co.uk)
But with some pets, it's open warfare when the carrier comes out. (pets.webmd.com)