expression
now that it's come to this; since things have reached this point
A formal, somewhat literary expression used to introduce a decisive action or resolution after a situation has developed to a critical stage. Often followed by a statement of determination or an unavoidable consequence.
かくなる上は、最後まで戦うしかない。
Now that it's come to this, we have no choice but to fight to the end.
かくなる上は、正直に話すべきだ。
Since things have reached this point, you should speak honestly.
More colloquial and commonly used in everyday speech; かくなる上は is more formal and literary.
Similar meaning but slightly more casual; かくなる上は carries a stronger sense of resolve or inevitability.
Derived from the classical Japanese adverb かく (thus, in this way) + なる (attributive form of なり, classical copula) + 上は (since, now that). The phrase literally means 'since it is thus,' and has been used since the Heian period.