The first season finale of The Walking Dead on AMC drew six million total viewers, its best numbers all season. The Walking Dead is already the most-watched drama series on cable in the 18-49 demographic. Four million of the finale’s viewers came from that demo.

The Walking Dead season 1 finale scored a 4.1 rating, and it won the night with the best ratings for original series on basic cable. The show is reportedly a similar hit overseas, where it’s shown in over 120 countries thanks to Fox International Channels.

AMC‘s high-profile premiere of The Walking Dead scored more than 5.3 million viewers Sunday night, with 3.6 million in the 18-49 demographic. Those numbers are good enough to make it the highest-rated pilot for any original cable series this year.

This is a huge win for AMC and for the creators of The Walking Dead in particular, who shopped their brutally realistic zombie drama to other broadcast and cable networks and were shot down. (Rumor has it the other networks balked because they didn’t think zombies had the same zeitgeist appeal of that other supernatural creature: the prettier, more angsty vampire.)

But the show came out of Comic-Con this year with a hot trailer and a huge buzz that refused to be ignored. If these kinds of ratings can be sustained with minimal drop-off (which seems unlikely, and I’ll explain why in a minute), then a second season is a foregone conclusion.

“The Walking Dead is that rare piece of programming that works on so many levels. It is legitimately great storytelling that is not only highly entertaining, but incredibly thought provoking as well. People who are familiar with the comic books know what’s coming, but suffice it to say, this is only the beginning of a long, intense, and powerful ride. Long live The Walking Dead,” said Joel Stillerman, AMC’s senior vice president of original programming, production, and digital content.

So here’s why I think The Walking Dead is a winner for the long haul. Cable TV has caught on to the same idea that foreign networks like the BBC have known for years — but which eludes the networks — is that shorter seasons lead to better storytelling. Everyone knows that serialized shows have greater depth, better characters, and more interesting stories than their standalone brothers — even the ones who won’t admit it. But networks can never seem to wrap their brains around how to make serialized shows commercial, because their business model is too committed to the 20+ episode season. It’s simple math: lower the episode count in a season, and you lower the requirement for an audience to keep up with an ongoing storyline.

The Walking Dead‘s first season consists of just 6 episodes. That’s an awfully easy commitment for a viewer to make.