There are a number of countries that have blocked YouTube. These countries are Brazil, Turkey, Germany, Libya, Thailand, Turkmenistan, China, North Korea, Iran, and Pakistan. This handy little 3-minute video explains why the popular video site was blocked in these countries at some point:
Do note that YouTube is not currently blocked in all of these countries, but the site was blocked in these places at one point in time. Some have very valid reasons and some very questionable ones (Some instances are YouTube preemptively blocking videos!). What I do know, however, is that every country with full access to cat videos is a better country because of it. Nobody should be deprived of things like this.