Easy.
The 'Net is built on a couple critical elements. The first is hardware. The original Internet backbone was built by the U.S. government, with private efforts coming along after it was opened up for non-government credential holders. Keep the original backbone restricted to U.S. government users and that will drastically slow the expansion of the private providers (Compuserve and MCI were able to use the U.S. government systems at the start of the their business). That, by itself, puts everything back by at least five, more likely ten, years.
The second critical element is universal access. The Web works because a user in Japan can connect to a data server in Australia, or the U.S., UK, ROK, etc. Stop that level of access and the World Wide Web literally stops. All that would be required is the U.S. government deciding that it was in the National Interet to prevent non-U.S. access to the backbone, same goes for other countries (rather like the DPRK, which has under 1,000 internet connections for a population of 24M people).
Another way to cut this off on the user side is for the telephone companies to grok to what is happening far earlier. It used to be that people had to actually pay for long distance charges for calls that went more than around 20 miles. A 5 minute cross country call could cost $15-20, and international three minute calls would damned near break the bank (a lot of people would only speak to relatives on the other side of the country one or twice a year). The various phone companies didn't see the monster on the horizon, and didn't push for regulation of internet usage (they actually could have had a decent case since Congress tends to HATE the government being in direct competition with private industry). If every minute you spent on line cost $1.00 there wouldn't be a lot of time spent surfing the 'Net. Eventually someone would find a way to get around the system (MCI managed it with AT&T, but in the end AT&T is still here and MCI was absorbed by Verizon), but it would take time.