conjunction
now that; since it is the case that
Formal written conjunction used to state a reason or premise for a conclusion. Often found in formal arguments, legal texts, or literary prose. Equivalent to 以上は or からには in modern spoken Japanese.
然る上は、この契約は無効と判断せざるを得ない。
Now that this is the case, we must conclude that this contract is invalid.
証拠が揃った然る上は、もはや言い逃れはできない。
Since the evidence is complete, you can no longer make excuses.
Compound of 然る (shikaru, 'such, like that') + 上 (ue, 'upon, after') + は (wa, topic particle). The phrase literally means 'upon it being such', and developed into a formal conjunction meaning 'now that' or 'since it is the case that'.