The American civil war was taking place while he was born. Abraham Lincoln was killed when Holmes was four years old and I don't believe that Abraham's death influenced him to become a serial killer. Worlds Columbian Exposition was held in Chicago in 1983 to celebrate the 400th anniversary of Christopher Columbus new discovery of the new world. During this time he would open a hotel and he knew a lot of people would come and this probably trigger him to think about murder because H.H Holmes is interested about death. Holmes was interested about death when bullies would take him to the doctors office(Holmes is scared of doctors) and they made him touched the skeleton. Other thing is that when Holmes bought the drugstore he would have a hard time to pay.later on the owner who sold the store to Holmes would get mad and use legal action against Holmes because he didn't pay on time and he and Holmes had a conflict. That's probably why he would start to kill because few months later the owner is never found again. This probably starts to trigger Holmes to start to kill due to obsessed with death.