Complex sentence: Willink arranged a deal with the Staatsspoorwegen in 1882, which immediately purchased five new steam trains, which ended up being a mistake as the Dutch government thought the SS would get too much market share on railroads.
Split into simpler sentences: Willink arranged a deal with the Staatsspoorwegen in 1882, enabling them to immediately purchase five new steam trains. This ended up being a mistake, as the Dutch government thought the SS would get too much market share on railroads.