A. briefly explain why one of the following options most clearly marks the shift away from isolationism in the 1910s that led to u. s. entry into world war i. preparedness movement tensions with mexico unrestricted submarine warfare b. provide an example of an event or development to support your explanation. c. briefly explain why one of the other options is not as useful to mark the shift toward u. s. entry into world war i.

Unrestricted submarine warfare clearly marks the United States shift from isolationism to interventionism. The US had several different involvements with the German who used unrestricted submarine warfare against either US citizens or the US military. For example, the Germans sunk the Lusitania, a British ship that contained American citizens. In this attack, over 100 American citizens were killed. This caused outrage among American citizens.

Tensions with Mexico is not a useful mark to show America's shift away from isolationism. The tensions between these two were only escalated due to the Zimmerman Telegram, which the Mexican government never technically received. Instead, the tensions lie more with the German government (who were responsible for sending this message).