At the age of 19, Van Asselt was drafted into the army, joining the Dutch Second Battalion of Yagers, and was stationed on the frontier between The Netherlands and Belgium.
He went to New Jersey and worked nine months for $35, then proceeded from Albany, New York by canal to Buffalo, New York, and thence by lakes and river to St. Louis, Missouri where he worked five months; then to Bloomington, Iowa, where he remained until the spring of 1850, when he joined a party of eight, including James Thornton and Charles Hendricks, to cross the plains to California, paying $100 for his food and transportation.
On the way the party of five fell in with L. M. Collins, who had a claim on the Nisqually River, Washington Territory, and was traveling with Jacob and Samuel Maple.
While crossing the river from that point Mr. Van Asselt accidentally shot himself in the shoulder and returned to St. Helens for treatment, where he remained for thirty days, then joined his friends on the Nisqually.
While staying with Collins he explored the surrounding country for a place to settle, but did not find anything satisfactory, so he decided to return to the Willamette Valley with his friends.
They were soon followed by the settlement of the Dennys and Terrys at Alki Point, and later by Mr. Yesler, who erected a sawmill, which provided work for the settlers in logging, as well as in farming.
In September, 1855, the Indian war broke out on White River, and after the killing of several settlers, those remaining fled to safety in Seattle.
Van Asselt joined Company A of the First Regiment, Washington Territory Volunteers, which was formed in Seattle to fight the Indians.