Perforce means because there was no other choice. Perforce we waited, must perforce agree, perforce abandoned.
It is formal and archaic, and it survives mainly in legal and literary prose where of necessity would do. It came into English as two French words, par force, by force, and closed up over time.
1adverbperforceBecause there was no other choice.
“With the bridge washed away, the villagers were perforce cut off for a week.”
perforce is a necessity.
From Old French par force, by force. The two words closed into one in English.
Old French
par force — by force
Middle English
par force
English, today
perforce
From Middle English par force, from Anglo-Norman -, from Old French par force (“by force”).
Etymology from Wiktionary, CC BY-SA
Practised in A Song of Ice and Fire