Hanoi is located not only by the sea on one side, but also by tropical rainforests or mountains on the other three sides. This geographical location is easy to defend but difficult to attack. This is an important factor in becoming the capital, after all, the capital is a political power that cannot be easily lost. In addition to being easy to defend but difficult to attack, there are also some evacuation routes that extend in all directions, from Hanoi to various parts of Vietnam, as well as Cambodia and Laos; The railway can directly reach Ho Chi Minh City in the south, the coastal city of Haiphong in the east, and the waterway can run eastward along the Red River to reach the sea.