Why did Lord Voldemort kill Harry Potter's family?

Answer 1

There was a prophecy that either Harry would kill Voldemort, or vice versa:"The one with the power to vanquish the Dark Lord approaches ... born to those who have thrice defied him, born as the seventh month dies ... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not ... and either must die at the hand of the other for neither can live while the other survives ... the one with the power to vanquish the Dark Lord will be born as the seventh month dies ..."

Answer 2

When Harry was born, there was a prophecy made by Professor Sybill Trelawney:

"The one with the power to vanquish the Dark Lord approaches ... born to those who have thrice defied him, born as the seventh month dies ... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not ... and either must die at the hand of the other for neither can live while the other survives ... the one with the power to vanquish the Dark Lord will be born as the seventh month dies ..."

The prophecy could have refered to one of two boys: Neville Longbottom or Harry Potter. Voldemort decided to kill Harry instead of Neville because he thought that Harry was more similar to him (because they were both half-bloods).

Answer 3

Voldemort killed a number of different people for different reasons. He killed his father and his fathers family for being muggles and for abandoning his mother when he found out she was a witch. He killed certain people to make certain horcrux's, he killed James and Lily to get to Harry because he heard a prophecy that he mistakenly interpreted, he killed many muggles or "mudblooods" just for sport, he killed out of anger and he killed to get ahead.

Answer 4

Ultimately, Voldemort has no regard for human life, so he just kills anyone whose death would be convenient for him.

Answer 5

Because they were part of the anti-Voldemort movement. But also, more specifically, because of the prophecy. This is explained in more detail in book 5.

Answer 6

He doesn't exactly try to "kill everybody". Mainly, Voldemort wants power; and he will kill people who he thinks are in his way in his quest for power.