Given the task definition and input, reply with output. In this task, you're given a story (which contains five sentences only). Your task is to find all the characters which are available in the given story.

Sentence1: Japan was building an Empire in Asia. Sentence2: The United States didn't support this. Sentence3: Japan needed to get America out of the Pacific. Sentence4: Japan decided on a pre-emptive strike. Sentence5: On December 7th Japan launched a surprise attack.

United states, Japan, America, Launched, Strike