Complex sentence: The Klan, who has a member inside the sheriff's department, burns a cross on Jake's lawn, causing an argument with Jake and his wife--that if Jake heeded Carl's warning this wouldn't had happened.
Split into simpler sentences: The Klan, who has a member inside the sheriff's department, burns a cross on Jake's lawn, causing an argument with Jake and his wife. That if Jake heeded Carl's warning, this wouldn't had happened.