Final answer:
The outbreak of the Spanish-American War in 1898 significantly influenced the U.S. Congress to declare Hawaii a U.S. territory due to its strategic location. President McKinley's re-submission of the annexation agreement as a resolution facilitated its passage, leading to Hawaii's territorial status in 1900.
Step-by-step explanation:
What Event Led to the Official Declaration of Hawaii as a U.S. Territory?
The formal annexation of Hawaii by the United States was largely influenced by the Spanish-American War that commenced in 1898. The strategic importance of Hawaii grew significantly as it was located between the U.S. West Coast and the Spanish-held Philippines, further underscored by America's intention to access Chinese markets. Despite the robust opposition from Native Hawaiians and anti-imperialist elements, President McKinley utilized a tactical legislative approach akin to Texas's annexation by converting the treaty into a resolution, lowering the Senate vote threshold from two-thirds to a simple majority.
Consequently, in 1900, Hawaii was declared a U.S. territory, establishing a unique territorial constitution that restricted suffrage to white male property owners, a provision not seen since before the Civil War.