Complex sentence: Despite their relatively scant altitude these mountains form an effective barrier between Thailand and Burma in their northern and central region, extending along the Kra Isthmus into the Malay peninsula.
Split into simpler sentences: Despite their relatively scant altitude these mountains form an effective barrier between Thailand and Burma in their northern and central region. The southern section of this extensive chain of mountains runs along the Kra Isthmus into the Malay peninsula.