Complex sentence: In recent years, Chiang Mai has become an increasingly modern city and that has attracted over 5 million visitors each year, of which between 1.4 million and 2 million are foreign tourists (depending on the year).
Split into simpler sentences: In recent years, Chiang Mai has become an increasingly modern city. It has attracted over 5 million visitors each year, of which between 1.4--2 million are foreign tourists (depending on the year).