What is the main conflict in The Book Thief?
I thought it was something like individual vs. society, because the book kinda describes how Liesel's life is affected by WWII.
However, I've seen other people with many other opinions, such as Liesel vs. Herself, Max vs. Society, etc.
Understand that in a novel the size of The Book Thief, there can be several conflicts happening at once and even multiple conflicts for the same character. The most overarching conflict in the context of the story, as you've stated, is WW2 and its affects on Germany (through the eyes of Death and a young girl). I like your idea of individual vs. society, as it focuses on the main character of the story, and shows how she handles living in a world in which much is beyond her personal control.
In comparison to "Liesel vs. herself," or "Max vs. society," your original idea is more of a main conflict. These other suggestions certainly are conflicts of the story, but I would not label them as prominent as Liesel vs. society. Consider also that when you examine Liesel vs. society, you will inevitable be looking at how she grows and changes ("Liesel vs. herself") and possibly even talk about how she views Max's struggle as well. You are definitely on the right track and have left yourself several options. Excellent work so far, and good luck with the rest.