I would like to know what other capitalistic system has existed out side the USA?
Unless there has been such a system, they must have failed for them to say it has never worked.
Almost all Western European countries went through a capitalist phase between mercantalism and embracing socialism-lite. It was European socialism that Marx wrong-headedly critiqued, setting the norm for the left in regarding economics as static, rather than dynamic. Likewise Canada.
Even Russia was briefly capitalist between the freeing of the serfs and the imposition of Bolshevism. On some measures, the present Russian Republic is more capitalist than the U.S. presently.
Japan is an example of off-and-on capitalism. There was a capitalist period c. 1920 (when parlimentary democracy and fascism was a near-run thing that went the wrong way) and again after the American occupation. South Korea is capitalist since being freed form the Japanese yoke. Australia is another example, and arguably India.