왜냐하면: Translates to "The reason why.." The difference is that it has "왜" in it which means "Why." For use, this phrase is used when explaining something, usually a situation that occurred or explaining a process of sorts. In sentences, "왜냐하면" is stated before the reason. English: I am hungry, because I did not eat lunch. Korean: 나는 (I am) 배가 고프다 (hungry), 왜냐하면 (because) 점심을 (lunch) 안 먹었다 (I did not eat). 때문에: A sort of "shortcut" for this phrase is to look at it as the negative version of "덕분에." It would translate to "Because of.." It is usually used in context with bad things that have occurred. This seems to be the one that is most similar to English's simple "because." In sentences, "때문에" is placed after the cause. English: I lost my boyfriend because of that girl. Korean: 나는(I) 저(that) 여자(girl) 때문에(because of) 내(my) 남자 친구를(boyfriend) 잃어버렸다(lost). ~로 인해서: This phrase would translate to "Due to.."/"The result of.." It is generally used formally to state an undeniable happening that something bad (usually a natural disaster/decline). One would not use this on a casual basis. This phrase is like "때문에" but more formal. When using this phrase, the cause is usually a common/proper noun placed before "인헤서." English: Due to the earthquake, many buildings collapsed. Korean: 지진(earthquake) 으로 인해서(Due to the) 많은(many) 건물이(buildings) 무너졌다(collapsed). 덕분에: This phrase would translate more to "Thanks to.." It is used with praise for something that caused a positive effect. Think positive with this one. This one is used AFTER the situation has occurred. You will notice that in sentences with "덕분에" the verbs will be in past tense because as I said before, it's used AFTER things have already happened. In sentences, "덕분에" is placed after the deed. English: I lived thanks to your help. Korean: 나는(I) 네가(your) 도와준(help) 덕분에(thanks to) 살았다(lived).

I'm sorry if my answer doesn't seem sufficient. The answer box only allowed up to 2000 characters so I had to cut out A LOT! Feel free to contact me if you have more questions!