All of Mexico came to me pretty easily, I think because I've lived in the Southwest U.S. my whole life. Juarez (which works without Ciudad btw) is well known as El Paso's neighbor across the Rio Grande and for its violence.
What embarrassed me was not coming up with two of the Swiss cities.
I thought Philadelphia or Boston would have made it for the USA. Cancun for Mexico. Xiamen for China. Bloemfontein for South Africa. Adelaide for Australia. Finally Santa Fe for Colombia
Fun fact: Cartagena (COL) was named after Cartagena (ESP), which used to be Carthago Nova, which was named after Carthago (TUN), which meant "New Town", which was a reference to Tyre (LBN).
Xi'an needs an apostrophe, by the way
What embarrassed me was not coming up with two of the Swiss cities.