Which of the following events was the final straw that caused the U. S. to declare war on April 7, 1917? a. Zimmerman telegram
b. Sinking of the Lusitania
c. Germany returned to unrestricted submarine warfare

The massacre at sand creek was an attack by a colorado militia on peaceful american indians. a colorado militia on a group of dakota warriors. american indians on peaceful white settlers. federal soldiers on a group of cheyenne warriors.