What cause Great Britain and France to declare war on Germany in 1939

Proponents of believe the government should right the wrongs of the past, but those against it believe it is a form of reverse discrimination.

Which of the following could affect the human population? a hurricane makes landfall on an uninhabited island. a deadly virus emerges that can pass from human to human. a civil war breaks out in italy. a solar eclipse occurs.

Could anything have been done through compromise to stop it, or did it have to happen?