Complex sentence: Spies settled in Chicago, where he became an upholsterer, involving himself in trade union activities due to the injustices he witnessed, Spies joined the Socialist Labour Party in 1877.
Split into simpler sentences: Spies settled in Chicago, where he became an upholsterer, involving himself in trade union activities. Due to the injustices he witnessed, Spies joined the Socialist Labour Party in 1877.