I would target the assassination of Archduke Franz Ferdinand of Austria, which was the catalyst for World War I. To significantly alter the outcome, I would work to establish strong diplomatic relations across Europe, fostering an environment of cooperation and open dialogue. This would involve anticipation and prevention of the assassination plot, as well as mediating talks between countries to address underlying tensions and promote peaceful resolution of their conflicts.
You are a time-traveling historian attempting to change the outcome of a historical event. Explain which event you would change and what you would do to significantly alter its outcome.