Final answer:
Spain, Russia, Britain, and the United States initially claimed the Pacific Northwest, but eventually only Britain and the United States remained as the main contenders for the territory.
Step-by-step explanation:
The three empires that claimed the disputed territory in the Pacific Northwest were initially Spain, Russia, Britain, and the United States. However, Spain and Russia eventually dropped their claims, which left Britain and the United States as the remaining contenders.
British claims were supported by discovery, exploration, and treaty rights, with the Hudson Bay Company playing a major role in colonizing the area through trade.
The United States' claims were also based on discovery, exploration, and treaty rights, and were further bolstered by the American settlers arriving during "Oregon Fever" which strengthened the U.S. claim to the Oregon Territory in the mid-1840s.
The three empires that claimed the disputed territory in the Pacific Northwest were Spain, Russia, and Britain. Spain made claims to the Philippines in the sixteenth century, while Russia and Britain had laid claim to various islands in the Pacific during the eighteenth and early nineteenth centuries.
These empires sought to expand their colonial possessions and exert influence in the region.