Complex sentence: Stevens felt that nationality of women should be included in that discussion and spearheaded the research, attended a preliminary meeting of the League of Nations and obtained their unanimous support of her proposal, and presented the data to the Pan-American Conference.
Split into simpler sentences: Stevens felt that nationality of women should be included in that discussion and spearheaded the research. She attended a preliminary meeting of the League of Nations and obtained their unanimous support of her proposal, and subsequently presented the data to the Pan-American Conference.