Final answer:
California entered the United States as a free territory in 1850.
Step-by-step explanation:
The state that entered the United States as a free territory in 1850 was California. In 1850, California was admitted as a free state under the Compromise of 1850, which aimed to maintain a balance between free and slave states. Under the Compromise, other territories gained in the Mexican-American War were allowed to choose whether they would enter the Union as free or slave states through popular sovereignty.
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