Here, the doer or the subject is not mentioned. So we need to add a subject that is generally used in these cases.

Given sentence is in past tense passive form.

Its rule is

Obj + Was/were + verb 3rd + subject.

Here, infinite (to go) and obliged are used. He is an object for the passive form. The subject is omitted. Generally, the circumstance is used as a subject in these cases.

Hence the active voice of a given sentence is

Circumstances obliged him to go.