Why was the Treaty of Paris controversial in the U.S. Senate?

The Treaty of Paris (1898) was highly controversial in the U.S. Senate primarily because it signaled a shift toward a policy of "imperialism" by the United States through the acquisition of the Philippines.12

While President William McKinley and his supporters viewed the islands as a strategic outpost for influence in the Far East and a base to protect U.S. commercial interests in China, many senators opposed the expansionist nature of the agreement. This debate reflected a fundamental tension regarding the ethical implications of the United States governing a foreign territory and its people without their consent, particularly as Emilio Aguinaldo had already declared the Philippines a provisional republic.21

Despite this vigorous opposition, the treaty was approved on February 6, 1899, by a margin of only a single vote. The controversy was underscored by the fact that the Philippine-American War had already commenced two days prior to the Senate's ratification, marking the beginning of a three-year conflict.12