Why did ancient Roman and ancient Greek civilizations give birth to democracy?

Marx once said that the ancient western countries were built on the ruins of clans, that is to say, when the western countries were formed, the blood relationship between the members of the country had no political significance. Therefore, when the slave countries in Greece and Rome were established, the form was similar to that in China during the Warring States Period, that is, aristocratic democracy and a hundred schools of thought contended in China. With the development of industry and commerce, it is impossible and unnecessary for western civilization, whose cultural source is Greece and Rome, to form a unified country like China from slave society to feudal society. Looking back at their situation in the slave society in western Europe, it is not difficult to find that the division of the feudal society in western Europe is another development form of their slave owners' aristocratic democracy, and European religious forces have long been a constraint of secular rights. Religious forces can be a tool for all kinds of secular forces to fight against kingship, but China is not. China has gone from clan to country, and the clan organization has not completely disintegrated. On the contrary, since the establishment of the Xia Dynasty, China has been "at home in the world", that is, a kind of patriarchal despotism, which unifies clan power and political power and realizes "loyalty" in the political field with filial piety in human nature. China is a typical agricultural country. In order to maintain long-term stability, it is necessary to determine a power center to exercise all state power in the form of feudal relatives, so this patriarchal autocracy has been continuously strengthened. In addition, China got rid of theological dogmatism earlier, and religious forces have been unable to manipulate secular kingship. Therefore, it is difficult for China to change the state power only by strength. Therefore, there is no democracy in China, but China is a big agricultural country.