New York’s Role in the War and its Aftermath

The U.S. entered Cuba’s war against Spain in April 1898 and ended it 100 days later. New York loomed large in the preparations for war and in battle. The city’s newspapers and magazines sold the war to the American public. Battleships produced in Brooklyn’s Navy Yard ferried New Yorkers to the fight and bombarded Spanish positions. And New Yorker Teddy Roosevelt became the war’s most vaunted commander. In 1901, following McKinley’s assassination, Roosevelt became the nation’s 26th president.
With the acquisition from Spain of Puerto Rico, Guam, and the Philippines, and the assertion of America’s right to intervene at will in Cuban affairs (the Platt Amendment), the U.S. became an overseas power. Victory also facilitated an extended U.S. military and commercial presence elsewhere in Latin America. Preeminent in this drive southward were the great corporations and banks headquartered in New York’s Wall Street.

Game of War, ca. 1900. New-York Historical Society, The Liman Collection, 2000.483. New Yorkers went wild over America's emergence as an imperial power, with their city as its de facto capital. They held a colossal celebration for returning heroes like Admiral Dewey; the artistic community collaborated in creating a mammoth triumphal arch (out of lath and plaster) at Madison Square. New York had come a long, long way from the colonial days when it feared the power of the Spanish Empire. 
Game of War, ca. 1900. New-York Historical Society, The Liman Collection, 2000.483.

Game of War, ca. 1900. New-York Historical Society, The Liman Collection, 2000.483. A century of acquisition and conquest—including lands taken from American Indians and Mexicans in the South and West—had turned the U.S. into a continental power. Now the nation had an overseas imperial presence as well. Acquiring the nation’s first overseas possessions provoked a major change in constitutional law. After the 1898 war, the U.S. Constitution no longer “followed the flag” into all newly acquired territories. In the Insular Cases (1901), the Supreme Court ruled that the U.S. could have possessions that might not become states or receive the “full panoply of constitutional rights.” Guam and Puerto Rico would become the longest-standing examples of such non-incorporated territories.
“Mr. Nobody from Nowhere,” is what Dr. Julio Henna—who fought Spanish colonialism and helped design the Puerto Rican flag—called his people’s new status in 1900. Four years later the court began to define the standing of Puerto Ricans when it ruled that a Puerto Rican woman named Isabel González could not be refused admission to New York since Puerto Ricans were not “aliens,” hence not subject to immigration laws. (Immigration officials had barred Ms. González, saying she was likely to become a public charge.)
In 1917, Congress made Puerto Ricans American citizens by passing the Jones Act, but retained a governance structure for the island that severely limited popular participation.
The National Publishing Company, The United States and its possessions, Puerto Rico, Cuba, Hawaii, Philippine Island and Alaska, 1900. New-York Historical Society.