Event 1 had an impact on Event 3 (the total population). Event 1 also causes Event 12 because it is part of the reason why President Wilson urged neutrality.
Event 9 (Americans unconcerned by foreign affairs) caused Event 11. Because Americans are not concerned about foreign affairs, they are also uninformed about the war, thus the outbreak of war takes them by surprise (Event 11).
Event 10 (the start of the war) causes many events, and understanding the relationship between Event 1 (immigration to the United States) and Event 3 (the total population in the United States) makes the reason for Event 12 (Wilson urges neutrality to occur).