AとあればB is a poetic and emphatic expression meaning “if” often used when B has to be done/is allowed in special circumstances A. Expressions like のため、必要、望み、命令 are common in A and expressions like ざるを得ない、しかない、なければならない follow in B. B is not used for requests.

Rarely, an old-fashioned とあらば form can be seen in older literature