Final answer:
The central idea developed in this passage is the search for the Northwest Passage and its significance for European explorers.
Step-by-step explanation:
The central idea developed in this passage is the search for the Northwest Passage and its significance for European explorers. The passage explains how various European countries, such as Spain, France, and Britain, sought to find an all-water route through the North American continent to gain access to the Pacific Ocean and trade with Asia. The passage also mentions that American explorers, like Lewis and Clark, took up the challenge to find the Northwest Passage, although it ultimately proved unsuccessful.