Historical trauma is described as collective emotional and psychological damage caused by traumatic events in a person's lifetime and across multiple generations according to Dr. Laurelle Myhra, an expert on Native American mental health. Native Americans experience historical trauma through the effects of colonization such as wars and battles with the U.S. military, assimilation, forced removal, and genocide. Outside of war and purposeful genocide, a senior lecturer on Native American literature and culture Dr. Carrie Sheffield maintains other causes are equally traumatic. She asserts that Native Americans experienced historical trauma through fatal epidemics, forced relocation to reservations, and the education of Native children at boarding schools. Even though many American Indians did not experience first hand traumatic events like the Wounded Knee Massacre, multiple generations are still affected by them. On December 29, 1890, over 200 Lakota were killed at Wounded Knee creek, South Dakota by U.S. soldiers. More than half were unarmed women and children. Unanswered pain from the Wounded Knee Massacre is still felt and has been related to present day substance abuse and violence. Experts of Native American trauma and mental health Theresa O'Nell and Tom Ball from the University of Oregon disprove the common misconception that historical trauma only occurs generations prior. They assert, contrastingly, that many current generations experienced trauma due to current violations of treaty obligations, land rights, racism, forcible relocation, and forced assimilation through federally-legislated boarding schools. In their interviews with Klamath and Umatilla tribal members, they observed intense emotional responses to recounted ancestral trauma. For them, one old woman weeped recounting the massacre of her grandmother's tribe, who was just a child at the time.