America was not multicultural(i.e. multi-racial) society at its founding, niether a one-person-one-vote-democracy which started only very recently.
America at its founding was a Republic, with only land-owners having the votes up until the Civil Rights Movement in the 60s. America was designed deliberately to avoid being a democracy actually - go read Thomas Jefferson!
Modern America was founded by Anglo-Dutch elites. Most of its earlier inhabitants, native Americans and some small groups of East Asians aside, were of one race - White European, one religion - Christianity, one tradition- JudoChristian, with one set of the corresponding social values, norms and even folk heros.
e.g. Within 2 generations, a recent Pole immigrant would have no obvious differences, both physically and intellectually, from say a Swede. That even applies to a large extent to the largest "diverse" immigrant groups to America in the modern history (prior to ww2), the Irish and the Italians in their millions.
Up until even 1960s, America was >90% premodinantly White European. Indeed the single largest ethnic group of America, till today, has been Germanic (yes, refers to ethnic Germans!), the ones with German-Anglo-Dutch ancestry in this case. So in a sense America by and large was, perhaps still is, a Germanic country in a nutshell.
America became world's superpower mostly on the back of:
1. single race by and large (Germanic-dominated White Europeans, with averaged high IQ of 100);
2. Republic (not Democracy);
3. vast per capita natural resources in the new world
4. "copycat" of most European technologies - yes, America was tagged as THE "copycat" in the 19th century by the Brits just like what they denounce China today. In fact a stamp of "Made-In-XXX" on the back of every products was deliberately invented by the Brits at a time to seperate "high quality Made-in-England" from "shoddy poor copycat Made-in-America".
5. "world factory", the title America enjoyed in 19th and 20th century until it passed it on to China.
(note: except point 3, today's China shares so many factors with yesterday's America)
Now, all these 5 major factors are either completely gone or have been severely undermined in recent years.
Historical fact: America became the world's superpower when it was White, and lost it / is lossing it, after it decided to "go multicutural multiracial" decades ago. - actually this is also the key point of Lee Kuan Yew in the OP.
Tomorrow's failed America will be more like Roman Empire at its end day, more akin to today "India" in fact
: multi-racial (and mixed races), multi-cutural with multi religions and multiple value systems and social econimical traditions, combined with large vote bank shams based on anti-meritocratic one-person-one-vote Democracy... Thomas Jefferson must be kicking in his grave.