Under the federal Copyright Act, an original work of authorship is copyrighted as soon as it is fixed in a tangible medium of expression (i.e. written on paper or an electronic medium like a hard or floppy disk, recorded on audiotape, videotape or film, drawn or painted on canvas, sculpted, etc.) You don't need to do a thing to have a copyright on your work.
You cannot copyright facts, ideas, speeches that have not been reduced to writing, titles, slogans, typography and ornamentation or information reproduced from commonly-available sources like government documents. Therefore, although you may copyright an article about an event, you cannot copyright the event itself to prevent or control what others write about it. You may write a history of Watergate, pulling together facts and events from 1972, but all you will own is your arrangement and expression of those facts, not the facts themselves.
Copyright is actually a bundle of distinct rights including the right to: reproduce the work, prepare derivative works based on the original material; distribute copies of the work; perform it or display it publicly. The owner may license others to do one or more of these things. For example, the owner of the history of Watergate can contract with Random House to publish a book, with TIME magazine to publish a condensed serialization, and with Paramount Pictures to produce a made-for-TV movie.