YOU SAID:
How on Earth did this happen?
INTO JAPANESE
一体どうしてこれが起こったのですか?
BACK INTO ENGLISH
How the hell did this happen?
INTO JAPANESE
どうしてこうなった?
BACK INTO ENGLISH
How did this happen?
INTO JAPANESE
どうしてそうなった?
BACK INTO ENGLISH
How did that happen?
INTO JAPANESE
どうしてこうなりました?
BACK INTO ENGLISH
How did this happen?
INTO JAPANESE
どうしてそうなった?
BACK INTO ENGLISH
How did that happen?
INTO JAPANESE
どうしてこうなりました?
it is unlikely that this phrase will ever reach equilibrium