> That's my point--just because places speak the same language doesn't mean they're culturally the same

Yes that's true. But I compare different Australian states – yes there are cultural differences even there, but they are pretty minor. If I compare US states – I'd say somewhat bigger cultural differences than between Australian states, for a bunch of reasons.

But still, my impression is, the cultural differences between US states aren't really that big by global standards. If you ranked countries by degree of internal cultural diversity, the US wouldn't be at the very bottom of the list, but it would be a long way from the top – I'd even say closer to the bottom than the top.

In some other countries, you have state/province/regional nationalist movements. Hard nationalists want their state/province/region to be an independent country – such as the Scottish National Party or Parti Québécois. You also have soft nationalists, who don't ask for independence, but seek greater autonomy while staying in the federation – such as Quebec's current ruling party, Coalition Avenir Québec; or the former ruling party of India's Punjab state, Shiromani Akali Dal. The US has a few state-based nationalist movements, but they've never been remotely mainstream, none of them have ever controlled a statehouse or a Governor's mansion. The existence of (practically significant) regional nationalism is a sign of greater interregional cultural difference, so countries which have it (such as Belgium, Canada, India, Spain, the UK) generally have significantly greater internal cultural diversity than those which lack it (such as Australia or the US).

> American politics isn't homogenous at all--that's just an artifact of political narratives being filtered through mass media in New York City. To use your abortion example (because I agree politics is an expression of culture):

Okay, but on the other hand that actually is an example of American politics being homogenous – because the whole country is arguing about the same things, of which abortion is a big one. Compare that to the UK – the Protocol is arguably the biggest political issue in Northern Ireland politics at the moment, in England it is a lot further down the list of people's concerns. A never-ending political debate in Quebec is about how to balance the promotion of the French language with the rights of the Anglophone minority – a topic that isn't very interesting to the average person in British Columbia.

Your example is just that in some parts of the US, the national abortion debate doesn't neatly line up with the two national parties. Meanwhile other countries have completely different debates in different parts of the country, and even completely different party systems in different parts of the country. All are examples of diversity, but your example is a little bit of diversity compared to other countries which have a lot lot more.

Also, your point about "mass media in New York City" is another example of homogeneity – US media is very centralised, national, tends to focus on national narratives more than regionally specific ones – that media homogeneity is both a symptom and a cause of cultural homogeneity. The BBC has its own division for Scotland – many people in Scotland (especially nationalists) complain that BBC Scotland is too London-focused and doesn't provide enough coverage of Scotland's own politics and culture – but even if those complaints are valid, no doubt it is doing a much better job of being regionally-focused than the US media does.