In ancient times, China has always been a continental power and generally did not expand to sea. There are countless islands around mainland China, such as Japanese Islands, Ryukyu Islands, Philippine Islands and Nanyang Islands, but after millennia, only two large islands remained in China: Hainan Island and Taiwan Island. During Ming Dynasty, China built a world-class navy, but navy went abroad not for expansion, but to promote country's prestige, canonization, and tribute diplomacy. At end of Ming Dynasty, it did not occupy additional islands for China. Why didn't ancient China seek to expand ocean?
The ancient countries and civilizations in world can be divided into three types, namely agricultural civilization, commercial civilization (maritime civilization), and nomadic civilization. Some people think that there is also a "fishing and hunting civilization." In fact, there are only fishing and hunting peoples, but there is no fishing and hunting civilization, because peoples who did not enter stage of fishing and hunting in Neolithic, when they entered era of civilization, fishing and hunting economy was replaced. Civilization here does not mean literacy, but access to the state stage.
The agricultural civilization is mainly located in river basin, which is why it is also called river civilization. The economy of an agricultural civilization is based on agriculture, and fiscal revenues of state are mainly received from farmers or serf laborers. Therefore, expansion of an agricultural country consists in expanding area of cultivated land, obtaining more expropriated population and strengthening power of country. For example, main direction of Egypt's expansion lies along Nile Valley, and countries of Western Asia mainly seek to occupy vast territories of oases.
China is most typical country of agricultural civilization, so main direction of expansion is basins of Yellow River, Yangtze, Pearl River and other rivers, among which Liaodong, western regions, Hehuang Valley and Hetao Plain, which are more suitable for agriculture, are also main directions of China's expansion. But if you go deep into prairies in north and jungles in Southeast Asia, you cannot expand. There are many islands around China, which in ancient times were sparsely populated, and it was easy to occupy them if desired. But for China, occupation of these islands can neither increase arable land nor greatly increase population, so ancient dynasties were unwilling to expand to the sea.
All overseas barbarian countries such as Annam, Champa, Goryeo, Siam, Ryukyu, Xiyang, Dongyang and small countries of Nanman are limited by mountains and seas and driven into a corner; there is not enough land for supply, and there are not enough people. order. If he doesn't know what to do and comes to disturb me, then it will be a bad omen. He is not concerned about China, and it is unfavorable for me to gather troops and attack lightly. I fear that future generations will rely on China's prosperity, greed for temporary military exploits, recruit troops for no reason, and harm lives. However, Hu Rong is approaching northwest of China, and world is a border trouble, so you need to select generals to train troops and be always ready. —— Emperor Ming Zu Xun by Zhu Yuanzhang
Expansion of commercial civilization is different from agricultural civilization, basically they need to occupy best transportation bases to get better business conditions. The first trading civilizations in world were Phenicia, Greece and Rome, directions of their expansion were mainly around Mediterranean Sea, for example, Phoenicia and Greece founded a large number of colonies in Mediterranean and Black Seas, and Rome turned Mediterranean Sea into an inland lake. During Age of Discovery, Europeans expanded their maritime expansion and established colonies around world.
Battle between Rome and Carthage for hegemony in Mediterranean
So how did impetus for overseas colonies come about? Taking Greece as an example, Greek mainland is not suitable for agriculture, but its industry and trade are developed and its population is relatively large, which puts a lot of pressure on its population. In order to move across ocean to occupy best sources of raw materials, trade markets, and transport country's surplus population, Greeks established new settlements along entire Mediterranean coast. In antiquity, many areas of Mediterranean were still backward, and it was relatively easy to occupy colonies. In modern times, Europeans used their ships and guns to occupy colonies in backward areas. For example, goal of Portuguese colonial expansion is to monopolize spice trade in East, while goal of Spanish colonial expansion is to monopolize gold and silver.
Another civilization is a nomadic civilization. The economy of a nomadic civilization depends on animal husbandry, therefore, nomadic peoples are fickle and operate in vast inland territories of Eurasian continent. The production of nomads is very unstable and lacks material accumulation. Therefore, they have formed a habit of robbing, and they always like to go to developed areas to rob. Nomads like to conquer everywhere, but when they conquer a place, if they stay and do not leave, they will be assimilated into local territory. At same time, nomads themselves were unable to build a long-term stable empire, and Xiongnu, Turks, and Mongols eventually collapsed. Therefore, their conquest lacked stability. For example, Mongolia almost conquered Eurasian continent and countries of Southeast Asia, but in the end they were left with pastures.
Does ancient China have a chance to become a maritime nation? Perhaps during Southern Song Dynasty, China gradually approached a maritime civilization, but essence was still agriculture. The later Yuan, Ming, and Qing dynasties cared even less about maritime interests. However, pirates of southeast coast of China have appearance of a maritime nation. Due to suppression of Ming maritime prohibition, they had to take risk of becoming "Japanese pirates" or "pirates". mainland and could only roam seas and islands.
During Ming Dynasty, China's pirate power increased and they established several commercial nations in Southeast Asia such as "Lanfang Republic". However, these countries were quickly wiped off face of earth by Western colonists. However, pirates also contributed to China's maritime expansion, for example, Zheng Zhilong occupied island of Taiwan and immigrated a lot here, laying foundation for Taiwan's annexation to China. If there is no interference from Western forces, I think that commercially civilized countries will gradually appear in Southeast Asia. Many of these countries may be dominated by Chinese, but they are also independent of China and do not belong to China.