Conversation so far:
What was significant about Kit Carson's third expedition?
In 1845, Kit Carson guided Frémont on their third and last expedition. They went to California and Oregon.
Why did Kit Carson and Frémont go on their third expedition?
Frémont made scientific plans, but the expedition appeared to be political in nature.

Question: How was it political?
Self-contained rewrite: How was Kit Carson and Frémont's third expedition political in nature?