。
We couldn't depart because of the storm.
Literal
Storm [because-of-ため] depart-could-not.
A bare subject-less sentence — Japanese simply omits the subject when it's inferable from context. The literal translation mirrors this by leaving the subject slot empty, exposing the structural fact that Japanese grammar doesn't require an overt subject. 出発できなかった is the suru-verb 出発する in its potential negative past form.