then; if so; if that is the case
Used to present a logical conclusion or hypothetical result based on a preceding statement. Similar to とすると, but slightly more formal or written.
See also: とすると
If he doesn't come, then the meeting will be postponed.
If what he says is true, this will be a serious problem.
If that is true, then it's a serious matter.
If that is so, we need to change the plan.
ならば is a more literary, general conditional marker, while とすれば specifically follows a stated premise to draw a conclusion from it.
とすれば marks an explicit supposition ('if we assume that'), whereas すれば more loosely links a condition to its result.
Derived from the conditional form of the quotative particle と plus the verb する. The exact historical development is uncertain, but it functions as a fixed conjunction meaning 'if so' or 'then'.