Army and warfare made their first appearance in Vietnamese history during the 3rd millennium BC. Throughout thousands of years, wars played a great role in shaping the identity and culture of people inhabited the land which is modern day Vietnam. Vietnam is regarded as one of the most militaristic countries in Southeast Asia, there is even a higher level belief Vietnam might be the most militaristic nation in Southeast Asia, and one of Asia and the world's most militaristic countries. The military history of the Socialist Republic of Vietnam began when Japan invaded French Indochina and soon defeated the French resistance. Since then, Vietnam has fought in many conflicts in Indochina. Hong Bang period Weapons are the most common Bronze Age artifacts found so far. The presence of arms in many tombs of upper-class people indicates the existence of a warrior class in Dong Son society during the Hong Bang period. Medieval period Warfare during this 500-year period (938–1407) was characterized by a combination of amphibious and land assaults. Owing to the fragmented terrain and long coast line of the country, maneuvers by boats were favoured by most military forces who had fought in Vietnam. Small-scale coastal and border raids were frequent. Domestic violence as well as foreign incursions were equally common. It is possible that during this period that Vietnam was at its height of power, first by defeating the Southern Han in 938 AD. Then they emerged and decisively defeated the neighboring Dali, Khmer Empire, Champa, and the Song. Mongol invasions of Vietnam In the 13th century, the Vietnamese defeated the Great Yuan dynasty of the Mongol empire three times, and it was seen as one of the most famous historical victories of Vietnam. In an extent, the Vietnamese successful repelling of Mongol invasions, had been recognized as the main factor which would have saved all Southeast Asia from Mongols. Cham–Vietnamese wars Early modern period Vietnam adopted firearms from the Ming dynasty in the late 14th century. The conquest of Champa was contributed to Later Lê dynasty firearm advantage. Around 15th-16th century, firearms started to gain dominance on Vietnam's battlefields. Rivaling feudal lords were quick to adopt these new deadly weapons. Tactics were changed to accommodate guns and cannons and soon the country had as many guns as it could afford. Throughout the time, the Vietnamese state also annexed the Southern region of the declining Khmer Empire which