Assertion (noun)

1. A confident and forceful statement of fact or belief.
2. The act of asserting oneself or one's rights.

Origin:

Mid 16th century: from latin assertio(n-), from the verb asserere (see assert).

Examples:

1. His assertion that he was innocent was met with skepticism.
2. The assertion that the company's products are safe has been proven to be false.
3. She made an assertion that she was right.
4. He made an assertion of his innocence.
5. The assertion of their rights led to the implementation of new policies.