In the mean time, Maha Nawrahta opened the southern front on 23 October 1765  in three directions. He had 20,000 to 30,000 under his command.  A small army invaded by the Three Pagodas Pass towards Suphanburi. Another small army invaded down the Tenasserim coast towards Mergui  and Tenasserim  town. However, the main thrust of his attack was at Kanchanaburi. His 20,000-strong main southern army invaded via the Myitta Pass.  Kanchanaburi fell with little resistance. The main reason for the quick fall of Kanchanaburi could be that the Burmese were more battle-hardened. But it could also be that the Siamese command miscalculated where the Burmese main attack would come from, and had not sufficiently reinforced the fort to withstand a major attack. Judging by the Siamese chronicles' reporting of the main attack route, the Siamese command appeared to have believed that the main Burmese attack would come from the Gulf of Siam coastline, instead of the most obvious and shortest route via Kanchanaburi. The Siamese sources say that Maha Nawrahta's main invasion route came from southern Tenasserim, crossing the Tenasserim range at Chumphon and Phetburi. The path is totally different from the Kanchanaburi route reported by the Burmese chronicles. Historian Kyaw Thet specifically adds that the main attack route was via the Myitta Pass.

Question: How many Maha Nawrahta opened the southern front?
Answer: three directions

Question: What is the Maha Nawrahta's main invasion route?
Answer: the Burmese were more battle-hardened

Question: Where was Maha Nawrahta's largest offensive?
Answer: Kanchanaburi

Question: What city did Maha Nawrahta conquer?
Answer: Kanchanaburi

Question: Who populated the city of Kanchanaburi?
Answer: the Siamese

Question: How many more maximum than minimum soldiers did Maha Nawrahta reportedly have for the southern front?
Answer: 10000

Question: Where did Maha Nawrahta travel through first, Kanchanaburi or Myitta Pass?
Answer: Myitta Pass

Question: What three areas did Maha Nawrahta's forces invade?
Answer: Mergui

Question: Why did Kanchanaburi fall so quickly?
Answer: Burmese were more battle-hardened

Question: Which different locations does Siamese sources and Kyaw Thet the main invasion route took?
Answer: Tenasserim range

Question: What are the different reasons for the fall of Kanchanaburi?
Answer: Burmese were more battle-hardened