The phrase' main cause' is unlikely to be helpful in discussing cultural differences. You would need to examine the whole history of each 'nation' which themselves are compendia of diverse social forces. Probably the main current
significant differences are reflected in comparison of political systems. As far as China is concerned, its recent coercive 'one child' policy has obviously been a major comparative issue, but hardly constitutes a 'cause' in its own right. Attitudes to 'the value of life' in general, such as the treatment of animals, or 'human rights', are probably far more significant differences which underpin the evolution of Chinese politics.
But we could talk in generalities forever. Modern global relationships fuelled by communication technology seem to indicate cultural convergence rather than difference. Snapshots of 'differences' are forever being superceded.