そこで details

Examples

so; that's when — introduces the action taken in response to the situation just described

何度なんどメールしても返事へんじがなかった。そこで、直接ちょくせつ電話でんわをかけてみた。

nando meeru shite mo henji ga nakatta. sokode, chokusetsu denwa o kakete mita.

I emailed again and again with no reply. So I tried calling directly. neutral

去年きょねんから部品ぶひんが手てに入はいりにくくなっています。そこで、設計せっけいそのものを見直みなおすことにしました。

kyonen kara buhin ga te ni hairinikuku natte imasu. sokode, sekkei sonomono o minaosu koto ni shimashita.

Parts have been hard to source since last year. So we decided to rethink the design itself. neutral

皆様みなさまから多おおくのご意見いけんをいただきました。そこで、本日ほんじつは新あらたな案あんをご提案ていあんいたします。

minasama kara ooku no go iken o itadakimashita. sokode, honjitsu wa arata na an o go teian itashimasu.

We have received a great many comments from you all. With that in mind, today I would like to put a new proposal to you. formal

それで
それで reports whatever followed, an outcome nobody chose included (雨あめが降ふった。それで、中止ちゅうしになった); そこで needs the second half to be a step somebody TOOK in response, so a spontaneous result after そこで does not stand — which is why a storyteller's next move takes そこで and a run of bad luck takes それで.
だから
だから hands the listener a conclusion to accept and can front an opinion or a refusal; そこで narrates the move actually made, so it is the connective of anecdotes and presentations (そこで、私わたしは考かんがえました) rather than of arguments.
すると
Both pick up a sentence already closed with a full stop, and they split what may follow — すると reports what the teller then saw happen, somebody else's deliberate move included (事情じじょうを説明せつめいした。すると、彼女かのじょは黙だまって財布さいふを出だした), while そこで introduces the move made in response, so a surprise after そこで and the teller's OWN chosen next step after すると both misfire.

で
Mid-sentence そこで is the pointer そこ plus the particle で — "there, at that spot" (そこで待まっていて) — and そこ need not be a place, since そこで初はじめて事ことの重大じゅうだいさに気きづいた points at a moment, which is how a non-volitional 気きづく comes to follow it; the sentence-initial connective names neither place nor moment, only the move made in response.