Short answers, pulled from the story.
The Spanish-American War was triggered by a combination of factors: the Cuban independence movement that began in 1895, the brutal Spanish reconcentration policy under General Valeriano Weyler, and the sinking of the USS Maine in Havana Harbor on the 15th of February 1898, which killed 266 American servicemen. Mounting public pressure and a congressional authorization forced President McKinley to seek military intervention.
The United States acquired sovereignty over Puerto Rico, Guam, and the Philippines through the Treaty of Paris signed on the 10th of December 1898. The U.S. also established a protectorate over Cuba and paid Spain $20 million for infrastructure in the Philippines. The war transformed the United States into a major world power with island territories spanning the globe.
The Spanish-American War lasted sixteen weeks, from April 21 to the 13th of August 1898. U.S. Ambassador John Hay famously described it as "a splendid little war." The formal peace treaty, the Treaty of Paris, was signed on the 10th of December 1898.
On the 1st of May 1898, Commodore George Dewey's Asiatic Squadron defeated the Spanish fleet under Admiral Patricio Montojo in Manila Bay. Dewey destroyed the Spanish squadron in a matter of hours with only nine Americans wounded. The victory gave the U.S. control of Manila's harbor and opened the path to capturing the Philippines.
Far more American soldiers died from disease than in combat. Fewer than 400 were killed in action, while 21,738 soldiers contracted typhoid fever alone, of whom 1,590 died. Yellow fever struck over 2,000 troops during the Cuban campaign. About 55,000 Spanish troops in Cuba, out of 230,000, were also incapacitated by illness.
The defeat was a profound national trauma in Spain, ending almost four centuries of Spanish presence in the Americas, Asia, and the Pacific. It sparked a broad philosophical and artistic reevaluation of Spanish society known as the Generation of '98. Spanish leaders had entered the war believing defeat was preferable to the political revolution that granting Cuban independence without a military loss would have triggered at home.