Why did the mad king kill Stark?

Related questions

1. Who is heir Jon Snow or Daenerys?
2. Is Meera Jons sister?
3. Who killed Neds sister?
4. Why did rhaegar and Lyanna fall in love?
5. Is Meera Reed Jon Snow's sister?
6. Why is Jon the heir to the Iron Throne?

Tags

1. #called
2. #freed
3. #prince
4. #lyanna
5. #rhaegar
6. #brother
7. #battle
8. #rickard
9. #scatter
10. #targaryen
11. #robert
12. #manages
13. #father
14. #decisive
15. #convinced
16. #demand
17. #aerys
18. #older
19. #usurp
20. #starks
21. #executes
22. #brandon
23. #trident