A quasi-alliance is a relationship between two states that have not formed an alliance despite sharing a common ally. It is an informal security arrangement that is not based on a formal collective defence pact, but it is instead based on tacit agreements. It is unique from an alliance as the states do not have this formal collective defence pact. These two states may remain unallied due to alliance hindrances such as historical animosity, but still share a common, powerful ally capable of diminishing the two states' security fears; security fears caused by a common threat.