MIHOP is an acronym for "Made It Happen On Purpose", specifically in regards to the 9/11/2001 attacks on the World Trade Center and Pentagon. It alleges that the U.S. parts of the government was the initiator of the 9/11 attacks. In short, it was an inside job. The milder theory, which holds that the U.S. government merely didn't do anything to prevent a known future attack is known as LIHOP (or "Let It Happen On Purpose").
MIHOP regards Dick Cheney as one of the masterminds of the plot. Some evidence MIHOP proponents bring to the table is the fact that NORAD fighter aircraft weren't scrambled, there were "exercises" taking place on the same day as the attacks that were supposed to the attacks or, in other cases, take away or confuse air cover, the WTC buildings (most particularly building number 7 (which contained government offices with classified information)) look like they were imploded, ownership of the buildings changed hands and a huge insurance policy was taken out on them, and a CIA money trail seemed to lead to some terrorists.
Although the United States of 2007 is crumbling, and the government can no longer keep law and order in the country, a large number of people still have access to the internet, whether through private lines or through mushrooming internet cafes catering to the poor. The internet is the main medium that has gotten this message across around the world so quickly, and the many videos made on the subject have turned "viral". Most Americans are already unhappy at the government for many reasons, including keeping them in the dark about peak oil beforehand and mismanaging the situation afterwards. Anti-government groups have also been springing up and two major coup attempts have already happened on the U.S. government, and the former state of Oregon has already seceeded, and MIHOP (and LIHOP) arguments have been claimed by these groups as a primary reason.
According to the latest polls available (December 2006), 92% of Americans (including Oregonians at the time) had heard of MIHOP and 59% believed that the U.S. government pulled off 9/11. The most common reason given why they thought the government had done so, was that it was an excuse to grab the Mideast oil. Notably, 22% of Americans polled (regardless of their stand on the factuality of the MIHOP theory), believed that if it could bring more oil to the ailing U.S., an internally planned 9/11 was worth it.