Complex sentence: Michael Dummett's research led him to conclude that-based on the lack of earlier documentary evidence-the Tarot deck was probably invented in northern Italy in the 15th century and introduced into southern France when the French conquered Milan and the Piedmont in 1499.
Split into simpler sentences: Michael Dummett's research led him to conclude that-based on the lack of earlier documentary evidence-the Tarot deck was probably invented in northern Italy in the 15th century. In either case, tarot cards were introduced into southern France from northern Italy when the French conquered Milan and the Piedmont in 1499.