 Residents voted for incorporation on March 14, 1989, and the city incorporated in February 1990.The Highline area, which includes modern-day SeaTac, Burien, Tukwila, and Des Moines, was settled by Americans in the mid-1850s.The federal government finished construction of a military road from Fort Steilacoom to Fort Bellingham in 1860, passing through the Highline area to the east of modern-day SeaTac.