Sentence:  During the trip Selkirk decided that the route through Illinois territory to Indiana and the eastern United States <WSD>was</WSD> the best route for goods from England to reach Red River and that the United States was a better source of supply for many goods than either Canada or England . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)