Usenet is not a UUCP network.
UUCP is a protocol (some might say protocol suite, but that's a technical point) for sending data over point-to-point connections, typically using dialup modems. Usenet is only one of the various kinds of traffic carried via UUCP, and UUCP is only one of the various transports carrying Usenet traffic.
Well, enough negativity.
Propagation of News
In the old days, when UUCP over long-distance dialup lines was the dominant means of article transmission, a few well-connected sites had real influence in determining which newsgroups would be carried where. Those sites called themselves "the backbone."
But things have changed. Nowadays, even the smallest Internet site has connectivity the likes of which the backbone admin of yesteryear could only dream. In addition, in the U.S., the advent of cheaper long-distance calls and high-speed modems has made long-distance Usenet feeds thinkable for smaller companies. There is only one pre-eminent UUCP transport site today in the U.S., namely UUNET. But UUNET isn't a player in the propagation wars, because it never refuses any traffic—-it gets paid by the minute, after all; to refuse based on content would jeopardize its legal status as an enhanced service provider.
All of the above applies to the U.S. In Europe, different cost structures favored the creation of strictly controlled hierarchical organizations with central registries. This is all very unlike the traditional mode of U.S. sites (pick a name, get the software, get a feed, you're on). Europe's "benign monopolies", long uncontested, now face competition from looser organizations patterned after the U.S. model.
Group Creation
As discussed above, Usenet is not a democracy. Nevertheless, currently the most popular way to create a new newsgroup involves a "vote" to determine popular support for (and opposition to) a proposed newsgroup. Newsgroup Creation, for detailed instructions and guidelines on the process involved in making a newsgroup.
If you follow the guidelines, it is probable that your group will be created and will be widely propagated. However, due to the nature of Usenet, there is no way for any user to enforce the results of a newsgroup vote (or any other decision, for that matter). Therefore, for your new newsgroup to be propagated widely, you must not only follow the letter of the guidelines; you must also follow its spirit. And you must not allow even a whiff of shady dealings or dirty tricks to mar the vote.