[SamPatt]

"The United States was neutral until the Japanese attacked Pearl Harbor in 1941, leading them to enter the war."

I'd say active is still better here.

[suyjuris]

I would disagree. This sentence is about the Unites States, not Japan, and the use of passive voice reflects that.

[selfmodruntime]

This is disingenuous. Removing the bad actor in this sentence removed part of the cause for the effect. Not an attack happened, a japanese attack happened.

[suyjuris]

I you feel that the actor is an important part of the sentence, you can include it in passive voice as well: “However, it was attacked at Pearl Harbor by Japan, and then chose to enter the war.”