Complex sentence: A popular uprising in Spain immediately spread to Junot's forces, which were accompanied by Spanish troops, and further instigated a popular uprising by the Portuguese that was brutally put down after having some minor successes.
Split into simpler sentences: A popular uprising in Spain immediately spread to Junot's forces, which were accompanied by Spanish troops. It further instigated a popular uprising by the Portuguese that was brutally put down after having some minor successes.