Image caption Jonathan Raban says the political split in the US is the result of a divide between rural and urban areas

British author Jonathan Raban has a theory about the lines which divide America - a theory he says the recent mid-term elections bore out once again.

He says it is becoming increasingly clear the US is not a patchwork of "red" and "blue" states - but rather a country composed of cities, which tend to vote Democrat, and their rural hinterlands, which lean Republican.

Seattle, where Raban has lived for some 20 years, is no exception.

It's sometimes hard to remember that Seattle began life as a logging town.

When the first white settlers arrived in 1851, they found a safe harbour in the sheltered waters of Puget Sound - a long, deep fjord that leads, by way of the Strait of Juan de Fuca, to the Pacific Ocean and transoceanic trade with Asia.

Within months of the settlers' arrival, Seattle's first industrial enterprise was Henry Yesler's steam sawmill, which opened for business on the waterfront in 1852, at the foot of a densely forested hill that rapidly turned into a field of raw stumps as it lost its massive, ancient Douglas firs to the settlers' axes.

The tree trunks were hauled down to the mill on a muddy trail called Skid Road, which became lined with honky-tonks and whorehouses, where the loggers spent the wages of their dangerous craft.

There may have been other skid roads elsewhere, but Seattle likes to claim that "Skid Row" is its own contribution to the American language.

Image caption Seattle has deep roots in the logging industry but has developed into a tech-heavy city in recent times

The seemingly inexhaustible supply of timber led Seattle into the boat- and ship-building business.

And when, in 1916, William Boeing, a 35-year-old timber millionaire, got the urge to branch out into aeroplanes, he bought up a bankrupt yacht building yard and hired its skilled carpenters to construct his lightweight boats with wings.

In Boeing's Museum of Flight in Seattle, one can see how these graceful early planes naturally evolved from the sleek sailing yachts that raced, and still race, on Puget Sound.

Llogical progression

So, too, the increasingly high-tech digital technology that was going into aircraft by the 1970s made a good fit with Microsoft's move here, from New Mexico, in 1979.

Timber to boats, boats to planes, planes to software, has been a logical progression for Seattle.

About Seattle 3.5m residents in the wider metropolitan area

About 250,000 households within the city limits

53% of adults have a college degree

Located 100 miles (160km) south of the Canadian border

Economic and cultural centre of Washington state

Port of Seattle offers a gateway to Asia

Before Microsoft and the information technology businesses (like Amazon, RealNetworks, and a host of others) that bob along in Microsoft's wake, Seattle was a regional city, closely integrated with its rural hinterland.

Since then, something close to a divorce has happened as the interests of the city and the countryside have diverged, and the acrimony and hard feelings that go with so many domestic splits have infected the politics of Washington state.

The "metropolitan area", centred on Seattle and spread around the edges of Puget Sound, has more than 3.5m people living in it, and so can narrowly outvote the other 3m people in the state.

The metropolitans tend to be Democrats (our "leftie" Seattle congressman, Jim McDermott, was re-elected on 2 November with an 83% share of the vote), while most of the farmers, ranchers, loggers, miners, rural developers and contractors are staunch Republicans.

Country versus city

At issue is the fundamental question of mankind's relationship with nature.

To many country dwellers, the mountains, plains, forests, and rivers of the state are a limitless resource of arable and grazing land, precious metals, timber and hydroelectricity - and some of the pious among them like to quote the Book of Genesis, in which God is said to give man "dominion" over "all the earth".

Image caption Environmental activists are often dubbed "Seattle liberals" by ruralists

To environmental activists (usually described by the ruralists as "Seattle liberals"), the magnificent geography of Washington state is a sacred space, a wilderness to be lovingly preserved and restored, as closely as possible, to its original "pristine" state.

And Seattleites have been inclined to treat the rest of their state as a giant park, a recreational facility for hikers, fly-fishermen, climbers, mountain-bikers, birders, and the like, for whom the traditional occupations of the countryside appear simply as rude blots on the landscape.

Pitched battles have been fought between the city and the countryside over such bones of contention as the habitat of the spotted owl (that battle resulted in the end of logging on National Forest land), gold mines, cattle grazing, dams on rivers (which block the passage of the declining runs of Pacific salmon to their spawning grounds), brush-cutting and wetlands setbacks.

In the course of this long and continuing conflict about land-use, rich, liberal, green, high-tech Seattle, with its high proportion of college graduates, has emerged as a post-regional city, deeply resented for its political power by people who live beyond the metro area, who once thought of Seattle as their own.

Profound division

So the rancorous, yelling, give-no-quarter style of recent American politics plays out here in the top left-hand corner of the US.

It's worth remembering that in the presidential election of 2004, every city in the nation with a population of more than 500,000 voted for the Democrats and John Kerry. George W Bush won re-election in the outer suburbs, the smaller towns, and the countryside.

The talk about "red states" versus "blue states" boils down to the fact that, as a general rule, states whose cities can out-vote their hinterlands are blue, and those whose hinterlands can out-vote their biggest cities are red.

Metropolitan Seattle, ultramarine in its political colour, dominates by sheer force of numbers the rest of Washington state, most of which is painted a bright scarlet.

In races for the US Senate, the state governorship and the presidency, Democrats here have (often very narrowly indeed) prevailed over Republicans in victories that have only exacerbated the tensions between the city and the country, and it's depressingly hard to see how this profound division might be healed, either here in Washington or in the nation at large.

You can hear more from Jonathan Raban on the forthcoming edition of BBC Radio 4's Americana programme, at 1915 GMT on Sunday.