There is that old adage in multi generational businesses that goes - "The first generation kicks off the business, the second generation builds upon what the first generation did, and the third generation squanders everything the first two generations did". In my 40+ years of business consulting I have actually seen this happen multiple times.
There must be something different about the Japanese cultural and philosophical outlook of building a business and handing it over to the next generation to carry on.
You have the numbers mixed up, Kongō Gumi had been founded in 578 AD so its run was over a millennia.
• It was started just right at the end of Kofun period when Japanese tribes started political centralisation (578 AD).
• It has survived unification of Japan under Tokugawa shogunate (1603 - 1868).
• It has survived forced opening of Japan to the outside world by the western forces (1854).
• It has survived World War I (1914 - 1918).
• It has survived World War II (1939-1945), ending in the near total destruction of the country.
Yet, when Japan survived to become a Trillion dollar economy; Kongō Gumi Co., Ltd. was liquidated and acquired by Takamatsu Construction Group (2006).
What does it take to build a Business which lasts over 1000 years now? Would humanity even last for next 1000 years with current geo-politics, inequality and hatred?
What part of WW2 resulted in near total destruction of the country? The two atomic bombs were tragic, but the near total destruction of two cities is a far cry from the near total destruction of a country.
No family stays poor for three generations.
And no family stays rich for three generations.
There are banks in Europe older than 400 years as well.