Seriously? I don't get that. Why does 60% of the US use CDMA when only 16% of the total world uses it?
I didn't know and decided to look it up, and basically found it interesting and got sucked in.
To begin with, it seems basically every country adopted their own standards for the first generation of cell phones -- there was very little compatibility. The US and Canadian carriers used AMPS (Advance Mobile Phone System) which was developed by Bell Labs. Most of the European countries developed their own standards, as did Japan. These standards all tended to be analog.
The Europeans realized it would help if they all were on the same system, so they developed a new digital standard (GSM) that all of the participating European countries would upgrade to. AMPS, however, was not compatible with GSM. Additionally, the US government (the FCC) required the companies with analog networks in the US to maintain those networks until 2008. So, it would be a major technical challenge for established US carriers to use GSM, as they would have to support both GSM and AMPS.
Two different standards were developed that worked with AMPS. Verizon went with IS-95, which was the first CDMA standard. AT&T used D-AMPS, which is also known as TDMA. Since both D-AMPS and GSM are types of TDMA networks, this eventually gave AT&T an upgrade path to switch to GSM; especially as analog customers upgraded to digital service.
The fact the US has more CDMA seems to have a lot to do with the size of the US. With plenty of US customers, cell phone makers were eager to develop phones to sell in the US, even though they used their own US standards. By contrast, cell phone companies were less eager to make phones for countries that had, by comparison, relatively few consumers. So, out of necessity, the European countries built a common standard that they could use to upgrade their different networks while the US was happy having their own standards.