It is not just a problem for France

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The biggest problem is not the system, nor is it war; it is the failure of racial management. They indiscriminately accepted non-white immigrants and refugees, bringing in too many people under the guise of managing former colonies and slaves. Now, after one or two centuries, they have become the underdogs.
Even the US has been facing significant side effects since the 1800s due to the indiscriminate acceptance of African Black slaves, and it has progressed so far now that it is beyond repair.
What is unfortunate about Western white-majority nations is that they lack the tenacious, "dogged" spirit found in Asians, so they are too relaxed. To put it nicely, they are easygoing; to put it bluntly, they are lazy.
Ultimately, one must run harder and work more diligently so that one's descendants and ethnic group can maintain a high standard of living, but because they fail to do so and simply spread out, these results occur.
I do not particularly like Chinese or Korean East Asian culture, but even so, one thing—nationalism and a mono-ethnic identity—will become a massive strength in the future. Compared to Western nations, Korea reacts very sensitively to foreign immigration and views it as a serious issue, so we will not end up like France, other European Western nations, or the US regarding multiculturalism.
Not just France, but most European white-majority nations like Germany and the UK, as well as wealthy developed nations like the US, Canada, and Australia—all white-majority populations will fall because they failed to manage their racial demographics.