The correct answer to this open question is the following.
Four incidents arousing anti-Spain sentiment in the United States included: Propaganda distribution against Spain, the sinking of the US Main, the letter from the ambassador, and stories in the newspapers against Spain.
The United States had been supportive of the independence movement of Cuba. He had sent some ships to the port la Havana, the capital city of Cuba, to closely follow the actions between Spain and Cuba when a mine sank the USS Main. Then what followed was a war declaration that started the Spanish-America War that started on April 21, 1898, and ended on August 13, the same year with a United States victory.
