Until then — referring to the time or state up to a certain point or event.
彼はそれまで特に問題を起こしたことがなかった。
He had not caused any problems until then.
私たちはそれまで毎日歩いて通学していた。
Until then, we had walked to school every day.
それまでは順調に進んでいたが、突然問題が起きた。
Everything had been going smoothly until then, but suddenly a problem occurred.
To that extent — indicating a degree or scope (up to that point).
彼の努力はそれまでに達した。
His efforts reached that level.
それまでに言ったことを忘れないでください。
Please don't forget what I said up to that point.
That's all there is to it / the end of it — used to indicate that something ends there or that's all.
相談はもう終わり。決定はそれまでだ。
The consultation is over. The decision stands as it is — that's the end of it.
彼女はもう話したくないと言って、それまでだ。
She said she didn't want to talk anymore, and that was that.