Complex sentence: Although the international trade through the Strait of Malacca had been favored since 6th century, the overland routes from the coastal towns in Southern Myanmar to the port towns of central Thailand were favored until the early Rattanakosin period.
Split into simpler sentences: Although the international trade through the Strait of Malacca had been favourite since 6th century. However the overland routes from the coastal towns in Southern Myanmar to the port towns of central Thailand were favourite until the early Rattanakosin period.