Admission to the Union is a function of three factors: the population of the prospective state; the local appetite for statehood; and the national political scene at the time of application. Here’s a quick comparison of Federal census counts for Oregon (est. 1859) and Washington (est. 1889):

1850: OR – 12,093, WA – 1,201

1860: OR – 52,465, WA – 11,594

1870: OR – 90,923, WA – 23,955

1880: OR – 174,768, WA – 75,116

1890: OR – 317,704, WA – 357,232

Washington’s regional geography played a significant role in the Territory’s lagging growth. Whereas Oregon’s fertile Willamette Valley feeds into the Columbia River and lies at the terminus of the Oregon Trail, early population centers in Washington were divided between the smaller Cowlitz watershed downstream from the mouth of the Willamette (Portland), dry regions upstream and east of the Cascades, and the Puget Sound (Seattle), which was easily accessible only by sea. The nineteenth century drivers for economic growth in the Puget Sound were raw exports like lime and lumber, which could only be exploited on an industrial scale with the development of external markets in California, Hawaii, Alaska, etc.

But population alone does not explain why Washington took fully three decades longer than Oregon – this is where politics come into play. Oregon, the last state to join the Union before the Civil War, was dominated in the 1850s by Northern Democrats who avoided the divisive “National Issue” of slavery by advocating for the status quo (Oregon was a free territory by the Missouri Compromise). The Kansas-Nebraska Act, together with the landmark Dred Scott case, later opened the free territories to slavery and spurred the local establishment to forestall the expansion of slavery in Oregon by pursuing statehood. As a result, Oregon drafted a Constitution and requested admission to the Union as a free state with the qualifier that free blacks be prohibited from immigrating to the new state. This controversial bid for statehood languished for some time in Congress, but was ultimately accepted when moderate Republicans and Democrats broke ranks with party hardliners.

Washington, on the other hand, had little impetus in the early years to pursue statehood, which would have ended their territorial tax benefits. When the territory finally did draft a constitution in 1878, the political climate in D.C. had soured, since Washington’s admission was widely expected to add Republican senators. A contested Presidential Election only two years earlier had ended in a comprise whereby the Republicans were granted the Presidency in exchange for an end to Reconstruction, the system by which they had maintained their dominance on the national stage since the Civil War. The resurgent Democrats were subsequently able to block the admission of new states until the Republicans regained the Presidency and both chambers of Congress in 1888. In the lame duck session that followed, the Democrats finally acquiesced to the simultaneous admission of four states, including Washington; two other states in the backlog followed shortly thereafter. So there you have it, politics is the main thing that held Washington back and pushed Oregon forward, though geography also lent a helping hand! If you’re interested in learning more about political trends in state admission, here is a conference paper on the subject.