I hate videos where the title is a question but could just be the answer, so I searched the answer instead of clicking: it's Germany's country code, .de, which has 16.1 million registered domains. The next two are .uk and .cn, which belong to the United Kingdom and China, with 10.6 million and 9 million domains, respectively.
The latest Map Men video is a bit light on the maps (there’s basically only one) but is still a fascinating look at how top level domains came to exist and not match the physical world.