GMO crops are not "banned" in any countries around the world in the normal sense of that word. Usually when something is banned for consumption, etc., it is because some problem emerged that needed a response. The history of regulation for biotech crops is quite different in that there were regulatory approval processes developed long before any such crops were commercialized. The goal was to try to anticipate any potential health or environmental issues and to make sure that no such problems were encountered. In the U.S. a "Coordinated Framework" for crop biotechnology regulation was set up with specific oversight responsibilities for the USDA, the EPA and the FDA. Other countries set up their own regulatory protocols. The goal was to ensure safety, and if any real safety issues had emerged after initial approvals, the system would have responded with a ban or some other restriction. In more than 20 years that has not been necessary.
Even well before any commercializations, there were activist groups that were opposed to the technology. Not for scientific issues, but primarily in opposition from a more philosophical position (anti-corporate. etc.) Those parties had different levels of influence from country to country depending on the degree to which politics drives regulation in each region. In much of Europe, very few farmers ever ended up being able to use these technologies and foods had to be labeled if they contained "GMO ingredients." In Europe many food industry players have chosen not to include GM ingredients, but that has been on a voluntary basis, not because of any governmental "ban." In Europe, GM crops were typically allowed, at least on a case-by-case basis as animal feeds and large quantities of such crops have since been imported from the countries where the farmers are allowed to grow them.
In the developing world there have been a number of successful campaigns by anti-GMO crops to block the production and even the import of GM crops and foods. Once again, these campaigns have not been driven by legitimate scientific questions and in many cases have been promoted by claims that are demonstrably false.
After more than two decades of commercialization without any health issues, the scientific community has been encouraging a streamlining of the regulatory process and a shift towards one the focuses more on the "product" itself than the "process" by which it was developed. Unfortunately, politics will continue to play a major role, particularly in some regions.