Learn Hardcore Swahili: Usumbufu ulikuwa mkubwa kiasi kwamba hatukulala usiku. - The disturbance was so great that we did not sleep at night.

Usumbufu can mean disturbance, trouble, inconvenience, or nuisance, depending on context. In this sentence, it most naturally means something like the disturbance or the noise/trouble that kept people awake.

So here it is not just a small inconvenience; it is something serious enough to affect sleep.

Why is the verb ulikuwa and not alikuwa or ilikuwa?

Swahili verbs must agree with the noun they refer to. The noun usumbufu takes the subject agreement u-, so the verb begins with u-:

u- = subject agreement for this noun
-li- = past tense
-kuwa = be

So ulikuwa means it was.

A native English speaker may expect one general word for it was, but in Swahili the form changes depending on the noun class of the subject.

Why is it mkubwa after usumbufu?