それではIf so, Well (then), In that case

では and じゃあ are both abbreviations of それでは, and used as conjunctions in Japanese. This structure may be considered as a combination of それ, the case marking particle で, and the binding (adverbial) particle は, but is commonly treated as a single word.

それでは has two primary functions. It can be used to continue in the same topic, showing that '(B) is a result of (A)'. Or it may be used to change the conversation topic completely, showing that '(A) is at a good point to become (B)'. In each of these cases, it can be translated as 'and with that' in English. 'If so', 'well then', and 'in that case' are also common translations.

The translation of 'in that case' is most commonly used when one person is making an assumption/drawing a conclusion about something that someone else has just said.

Fun Fact

それでは, では, and じゃあ are also frequently used as a polite way to say 'goodbye'. In these situations, it comes across in a similar way to 'well…. I best be off' in English.