Was the historical King Arthur Celtic or Roman?

Did the founding fathers attempt to found the United States on Christian or on Deist principles?

Was the use of the atomic bomb necessary?

Were Santa Anna and the Mexican government justified in attempting to crush the Texan revolution?

Was intelligence intentionally withheld from Pearl Harbor leaders to make the attacks on the base a success?

"Was the historical King Arthur Celtic or Roman?"

I think this is a bad choice because it's based upon a presumption, that there was a historical Arthur. "Was there a historical Arthur?" may be a better question, the evidence for however would fit on a postage stamp, so perhaps not a great choice.

"Was intelligence intentionally withheld from Pearl Harbor leaders to make the attacks on the base a success?"

Not a very scholarly subject, to much in the UFO, Moon landing fakes, conspiracy theory mold.

These three seem very academic to me, undoubtably have a wealth of material and opinions around.

"Did the founding fathers attempt to found the United States on Christian or on Deist principles?"

"Was the use of the atomic bomb necessary?"

"Were Santa Anna and the Mexican government justified in attempting to crush the Texan revolution?"

The question you should ask yourself is what subject would you enjoy researching and writing about the most.

Another is which subject do you already know the most about and already have some theories upon.

Then I'm sure people may be able to suggest other questions.