CHARLOTTE, N.C. — A U.S. Army soldier shared a racist, violent reason for joining the service on Instagram and engaged in online extremism while stationed at Fort Bragg in North Carolina, according to federal investigators. “I serve for combat experience so I’m more proficient in killing (racial slur),” Killian Mackeithan Ryan wrote about Black people on one of his five Instagram accounts, court documents filed in late August state. With these accounts, investigators say Ryan messaged other accounts “associated with racially motivated extremism,” according to an affidavit. Ryan’s online activi…