Similar radio services exist in many countries around the world. Frequencies, power levels, and modes (such as FM, AM and SSB) may vary from country to country, and usage of foreign equipment may be illegal. However, many countries have adopted the American frequencies.
In Canada, the "General Radio Service" has the identical frequencies and modes as the United States "Citizen's band", and no special provisions are required for either Canadians or Americans using CB gear while traveling across the border.
In Europe, the CEPT adopted the North American channel assignments, except that FM is used instead of AM. Some member countries permit additional modes and frequencies. Germany also has 40 unique channels at 26 MHz for a total of 80. Before CEPT, most of the member countries used some subset of the 40 USA channels.
New Zealand and Japan have unique allocations that don't correspond to any other country.
Using radios outside their intended market can be dangerous as well as illegal.