The sister city concept grew out of getting better economic ties and trade after WWII. Below is a list of Denver's sister cities. Brest, France is the second oldest sister city in the US. There was mentioning of Takayama in the early civics lessons in the 5th or 6th grade in the early 60's.
Joelene
Brest, France (1948)
Takayama, Japan (1960)
Nairobi, Kenya (1975)
Karmiel, Israel (1977)
Potenza, Italy (1983)
Cuernavaca, Mexico (1983)
Chennai, India (1984)
Kunming, People's Republic of China (1985)
Axum, Ethiopia (1995)
Ulaanbaatar, Mongolia (2001)