Bellinghamster here. And I happen to live on the grounds of a historic mansion full of old newspaper articles and history books about the region. The answer to your question:

The coastal area between Seattle and Vancouver was not blessed with large seawater ports.

In the mid-late 19th century, the coastal Pacific Northwest was serviced solely by tall ships. Seattle and Vancouver had huge, deep ports that supported plenty of import/export/transportation. Ships would arrive with goods and materials for consumers, builders, and business, and would leave loaded with timber and coal. These ships also ferried people to and from distant ports. Ships' arrivals were always announced in local newspapers so locals knew what (and sometimes who) was coming.

The region was blessed with plenty of raw material to export, so Seattle and Vancouver grew quickly. The area in between (Bellingham for example) had one small port which serviced just a few ships at a time. They built service jetties to offload raw material to support another ship or two, but that was it.

As a consequence of the area's limited capacity, there was limited access as well. US Hwy 99 ranged north from Seattle to the Canadian border, but it was a difficult, unpaved road that was often affected by rockfall in the Chuckanut mountains. It wasn't paved until the 1930's. And then it was still a sketchy 2-lane road.

I-5 from Seattle to Bellingham wasn't completed until 1969. At that point, the region grew quickly. It is now one the most desirable locations in America, hitting the Top 10 in innumerable magazine surveys.

EDIT: Highway 99 was paved between Everett WA and Bellingham in 1921, not 1930. The paving to the Canadian border was finally finished in 1930.

EDIT 2: I looked in the mansion for the history books and Bellingham Bee newspapers. Staff have removed them to the locked archive building for safekeeping. I have no access. Sorry. My post is therefore predicated on my own reading which I am unable to cite. Mods may treat my post as they see fit.

Seattle really isn't that huge of a city and most of its growth has been recent. The Seattle Metro Area is only the 15th biggest in the US and the city itself is only 20th. Vancouver is even smaller. On the other hand going from Boston to DC goes through 4 of the top 10 metro areas in the US with a total population many times that of Seattle and Vancouver.

Compared the urban east coast Seattle was basically a small logging town until the Gold Rush caused an influx of people in the late 1800's into the 1900's. After that the population only went from about 230k in 1910 to 500k by the 1980's. Seattle's somewhat status a global city is really only a recent phenomenon.

Much of that is a factor of time. European settlers established cities in the East Coast before the Northwest was even fully explored. New York already had over a million people before Seattle was even had 1,000. Later, as waves of migration arrived from Europe they almost always arrived on the East Coast as cross ocean travel at the time was sea based and sailing to the West Coast was a long and dangerous journey. There were Chinese and other Asian migrants to the West Coast, but their numbers paled in comparison to what was arriving from Europe on the West Coast and their immigration was eventually banned for decades beginning in 1882.

So you simply had more people and since migrating further west was difficult, most just stayed put driving up density along the coast and Great Lakes. Before the Transcontinental railroad, getting to the West Coast took many months and required extensive planning. While hundreds of thousands of people did make the trip, they were a fraction of the millions who were building big cities in the East.

When people started moving West in earnest in the mid to late 1800's California had many advantages over Washington. While Washington had a Gold Rush of it's own, California had one 50 years earlier which brought 300,000 people to the State before Seattle was even incorporated. The first Transcontinental railroad went to San Francisco in 1869 whereas the Northwest (Tacoma) wouldn't get a line until over a decade later. California also had better farming and mining and benefited from the discovery of oil in the late 1800's. Between the railroads and easier sea travel getting these goods out was also easier in California than Washington. That head start is reflected in the greater population between San Francisco, CA and San Diego, CA.

Another major factor is that Seattle and Vancouver are in different countries. While some people certainly do live in one and work in the other, that isn't something most people would be willing to do. Even with things like NEXUS, crossing the border is still a pain and not something you'd want to do 5 days a week. You do see a lot of density in the area around Seattle and Tacoma.

Cities arise in places that offer the most advantages for economic activity. Being near scenery only gives rise to resort towns; proximity to other cities typically only creates suburbs or manufacturing satellite cities.

To grow large adjacent cities, harbors need not just shelter from ocean storms but also good connections to their hinterland. Along the East Coast, 19th century canals, easy-grade wagon roads, and multiple railroads provided those connections to many harbors. In the Pacific Northwest, only a few railroads were able to connect the hinterlands through the mountains to Pacific harbors, and those railroads chose to reach the Pacific at Vancouver, Seattle, Tacoma, and Portland.

The classic coastal port city grows from a combination of harbor activity, manufacturing using power from the river flowing into the bay that serves as harbor, and from the need to transfer cargo from one mode of transport to another. Since you're already moving stuff around, may as well set up factories that can add value to some of the raw materials arriving from the hinterland before shipping them out again—or warehouses that make money by combining and dividing piles of stuff. That classic entrepôt function is much easier to recognize in an old-fashioned break-bulk harbor; new containerized harbors like Prince Rupert don't see nearly as much spinoff economic activity.

As for the other areas you mention, I'd say that the 140 miles between Seattle and Vancouver has just as many smaller cities as you'd find in a similar length of the California coast or between Quebec and Windsor.

Hey, friends,

This is just a reminder that we require answers in AskHistorians to answer the question itself. An answer that is in-depth and comprehensive will by its very nature address any inaccuracies or misleading phrasing in the original question.

Don't clutter up the thread with your pet example of a non Seacouver city in the PNW--unless you can also discuss patterns of West Coast urbanization over time.

Thanks!