There are many regimes throughout the world who really want to make it very difficult, or preferably impossible, for their citizens to run software which allows them to browse the Internet anonymously.
Iran is doing SSL-handshake fingerprinting in order to prevent their citizens from using Tor-connections.
China is blocking the entire Tor-network and quite a large number of Tor bridges. Users who can not access the Tor-network directly can use it through bridges – but it is possible to block all of those too because there are too few of them.
Few countries have managed to block the entire Tor network and all bridges. It seemed impossible. But how Egypt’s done it. It’s all blocked. How did they do it? Simple: They simply cut the whole country off from the Internet..