Learn Danish: Reglen var streng, så vi skulle blive hjemme. - The rule was strict, so we had to stay at home.

Both skulle (past tense of skal) and måtte (past tense of må) can translate to "had to". However, skulle is often used when a rule, duty, or external plan dictates the action, similar to "were obliged to" or "were supposed to". Because a strict rule is enforcing this action, skulle sounds very natural for this kind of obligation.

I thought blive meant "to become". Why does it mean "stay" in this sentence?

You are right that at blive often means "to become" (like in han bliver glad - he becomes happy). However, it is also the standard Danish verb for "to stay" or "to remain". When it is followed by a location word like hjemme, it almost always translates to "stay".

Why use hjemme here instead of just hjem?

Danish distinguishes between movement and standing still. Hjemme means you are already located at home (stationary). Because the action is staying (blive), we use the stationary form. If you were moving toward your house, you would use the motion form, hjem (for example, vi gik hjem - we went home).

The dictionary says "rule" is regel. Why is "the rule" spelled reglen without the middle 'e'?