expression
until then; up to that time
Refers to a point in time before which something continues or after which something changes. Often used in narratives or when contrasting past and present.
それまで彼は一度も海外に行ったことがなかった。
Until then, he had never been abroad.
それまで静かだった部屋が急に騒がしくなった。
The room, which had been quiet until then, suddenly became noisy.
expression
Expresses degree or extent, often in a negative or surprised tone. Common in phrases like それまでか (is that all?) or それまでだ (that's the end of it).
彼の努力もそれまでだった。
His efforts ended there (were only to that extent).
どんなに頑張っても、運がなければそれまでだ。
No matter how hard you try, without luck, that's all there is to it.
expression
the end of it; all there is to it
Used to indicate that something has reached its limit or conclusion, often with a sense of finality or resignation. Frequently appears in set expressions like それまでだ or それまでよ.
ここで諦めたら、すべてはそれまでだ。
If you give up here, that's the end of everything.
人生は一度きり、死んでしまえばそれまでよ。
You only live once; once you die, that's it.
Compound of それ (that) and まで (until, to the extent of). The combination naturally yields temporal and extent-related meanings.