I grew up near the CA Inland Empire and now live near the WA one. I don't really think of these areas as having a cultural or political connection. However, both areas seem to date to the late 19th century, when rail and industrialization made agricultural and extraction economies viable.
So I'm wondering if it's just a neat coincidence or if the phrase "inland empire" might have had some shared significance to the people who named the regions.
Thanks for your time!
I can't really speak to California's Inland Empire, but as a heritage worker and high school teacher in BC's Interior, I'll try my hand at answering Washington's Inland Empire and more broadly the term 'Inland Empire' in general - it gets applied in more places than you'd think!
Ultimately it's a story of the intersection of developing media and the drive to map and survey the inland parts of the former Oregon Territory, both the British and later Canadian, and United States surveys sought to create accurate maps of their new territories, especially after the Oregon Treaty in 1846. What you might notice if you ever look at maps of the interior of Washington, Oregon, and British Columbia up until the 1890s is how empty of settlement they are outside of major travel routes, and you don't even see regional names emerging in these regions until the 1870s and 1880s, and the idea of broader regional identities like an "Inland Empire" wouldn't emerge until much later.
In fact, it is newspapers where you first see the term "Inland Empire" used, well before any concerted settlement of the interior of the Pacific Northwest. The earliest uses in the region are in late 1870s and early 1880s in newspapers in Seattle and Vancouver to refer the opportunity available in settling the inland parts of the region. However, the term 'Inland Empire' appears in Idaho, Montana, and the Dakotas as early as 1869 as terms for regions also recently opened for settlement there.
It doesn't seem to be until the late 1890s and first few decades of the 20th century that any coherent idea of "The Inland Empire" emerges in the Okanagan/Okanogan area, with Spokane at its heart. Indeed, the local papers like the Spokane Press and Spokane Woman regularly making reference to the region as such. In the same period, British Columbia is also referring to the regions surrounding the developing centres of Kamloops and Kelowna as the "Inland Empire," and are even applying it to maps of the time. In 1944, photographer Erskine Burnett even publishes an album of his photos from the BC Interior called "BC's Inland Empire" and the name continues to be used in both Washington and B.C. until the 1960s. By then, the strong regional identity seems to be diminishing as people migrated in the postwar era, and today the name endures mostly around Spokane, especially in relation to heritage or regional identity.
If I'm to go outside my knowledge on this, I would even hazard that California's "Inland Empire" could have a similar origin, as the area was settled expanding out from the already major centres of San Jose and Los Angeles, and seems to be a term that was used outside even California and the Pacific Northwest to refer to inland areas of new settlement.
Further Reading:
Morissey, Katherine G. Mental Territories: Mapping the Inland Empire. Ithaca: Cornell University Press, 1997.
Burnett, Erskine. B.C.'s Inland Empire. Self-published, 1944.